Keith Number/Examples/754,788,753,590,897
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Examples of Keith Number
$754 \, 788 \, 753 \, 590 \, 897$ is a Keith number:
- $7, 5, 4, 7, 8, 8, 7, 5, 3, 5, 9, 0, 8, 9, 7, \ldots, $
Proof
By definition of Keith number, we create a Fibonacci-like sequence $K$ from $\paren {7, 5, 4, 7, 8, 8, 7, 5, 3, 5, 9, 0, 8, 9, 7}$:
\(\ds K_0\) | \(=\) | \(\ds 7\) | ||||||||||||
\(\ds :\) | \(\) | \(\ds \) | ||||||||||||
\(\ds K_{14}\) | \(=\) | \(\ds 7\) | ||||||||||||
\(\ds K_{15}\) | \(=\) | \(\ds K_0 + K_1 + K_2 + K_3 + K_4 + K_5 + K_6 + K_7 + K_8 + K_9 + K_{10} + K_{11} + K_{12} + K_{13} + K_{14}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 7 + 5 + 4 + 7 + 8 + 8 + 7 + 5 + 3 + 5 + 9 + 0 + 8 + 9 + 7\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 92\) | ||||||||||||
\(\ds K_{16}\) | \(=\) | \(\ds 2 \times K_{15} - K_0\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 92 - 7\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 177\) | ||||||||||||
\(\ds K_{17}\) | \(=\) | \(\ds 2 \times K_{16} - K_1\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 177 - 5\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 349\) | ||||||||||||
\(\ds K_{18}\) | \(=\) | \(\ds 2 \times K_{17} - K_2\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 349 - 4\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 694\) | ||||||||||||
\(\ds K_{19}\) | \(=\) | \(\ds 2 \times K_{18} - K_3\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 694 - 7\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 1381\) | ||||||||||||
\(\ds K_{20}\) | \(=\) | \(\ds 2 \times K_{19} - K_4\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 1381 - 8\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2754\) | ||||||||||||
\(\ds K_{21}\) | \(=\) | \(\ds 2 \times K_{20} - K_5\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 2754 - 8\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 5500\) | ||||||||||||
\(\ds K_{22}\) | \(=\) | \(\ds 2 \times K_{21} - K_6\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 5500 - 7\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 10 \, 993\) | ||||||||||||
\(\ds K_{23}\) | \(=\) | \(\ds 2 \times K_{22} - K_7\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 10 \, 993 - 5\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 21 \, 981\) | ||||||||||||
\(\ds K_{24}\) | \(=\) | \(\ds 2 \times K_{23} - K_8\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 21 \, 981 - 3\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 43 \, 959\) | ||||||||||||
\(\ds K_{25}\) | \(=\) | \(\ds 2 \times K_{24} - K_9\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 43 \, 959 - 5\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 87 \, 913\) | ||||||||||||
\(\ds K_{26}\) | \(=\) | \(\ds 2 \times K_{25} - K_{10}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 87 \, 913 - 9\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 175 \, 817\) | ||||||||||||
\(\ds K_{27}\) | \(=\) | \(\ds 2 \times K_{26} - K_{11}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 175 \, 817 - 0\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 351 \, 634\) | ||||||||||||
\(\ds K_{28}\) | \(=\) | \(\ds 2 \times K_{27} - K_{12}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 351 \, 634 - 8\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 703 \, 260\) | ||||||||||||
\(\ds K_{29}\) | \(=\) | \(\ds 2 \times K_{28} - K_{13}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 703 \, 260 - 9\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 1 \, 406 \, 511\) | ||||||||||||
\(\ds K_{30}\) | \(=\) | \(\ds 2 \times K_{29} - K_{14}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 1 \, 406 \, 511 - 7\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \, 813 \, 015\) | ||||||||||||
\(\ds K_{31}\) | \(=\) | \(\ds 2 \times K_{30} - K_{15}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 2 \, 813 \, 015 - 92\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 5 \, 625 \, 938\) | ||||||||||||
\(\ds K_{32}\) | \(=\) | \(\ds 2 \times K_{31} - K_{16}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 5 \, 625 \, 938 - 177\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 11 \, 251 \, 699\) | ||||||||||||
\(\ds K_{33}\) | \(=\) | \(\ds 2 \times K_{32} - K_{17}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 11 \, 251 \, 699 - 349\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 22 \, 503 \, 049\) | ||||||||||||
\(\ds K_{34}\) | \(=\) | \(\ds 2 \times K_{33} - K_{18}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 22 \, 503 \, 049 - 694\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 45 \, 005 \, 404\) | ||||||||||||
\(\ds K_{35}\) | \(=\) | \(\ds 2 \times K_{34} - K_{19}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 45 \, 005 \, 404 - 1 \, 381\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 90 \, 009 \, 427\) | ||||||||||||
\(\ds K_{36}\) | \(=\) | \(\ds 2 \times K_{35} - K_{20}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 90 \, 009 \, 427 - 2 \, 754\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 180 \, 016 \, 100\) | ||||||||||||
\(\ds K_{37}\) | \(=\) | \(\ds 2 \times K_{36} - K_{21}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 180 \, 016 \, 100 - 5 \, 500\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 360 \, 026 \, 700\) | ||||||||||||
\(\ds K_{38}\) | \(=\) | \(\ds 2 \times K_{37} - K_{22}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 360 \, 026 \, 700 - 10 \, 993\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 720 \, 042 \, 407\) | ||||||||||||
\(\ds K_{39}\) | \(=\) | \(\ds 2 \times K_{38} - K_{23}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 720 \, 042 \, 407 - 21 \, 981\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 1 \, 440 \, 062 \, 833\) | ||||||||||||
\(\ds K_{40}\) | \(=\) | \(\ds 2 \times K_{39} - K_{24}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 1 \, 440 \, 062 \, 833 - 43 \, 959\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \, 880 \, 081 \, 707\) | ||||||||||||
\(\ds K_{41}\) | \(=\) | \(\ds 2 \times K_{40} - K_{25}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 2 \, 880 \, 081 \, 707 - 87 \, 913\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 5 \, 760 \, 075 \, 501\) | ||||||||||||
\(\ds K_{42}\) | \(=\) | \(\ds 2 \times K_{41} - K_{26}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 5 \, 760 \, 075 \, 501 - 175 \, 817\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 11 \, 519 \, 975 \, 185\) | ||||||||||||
\(\ds K_{43}\) | \(=\) | \(\ds 2 \times K_{42} - K_{27}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 11 \, 519 \, 975 \, 185 - 351 \, 634\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 23 \, 039 \, 598 \, 736\) | ||||||||||||
\(\ds K_{44}\) | \(=\) | \(\ds 2 \times K_{43} - K_{28}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 23 \, 039 \, 598 \, 736 - 703 \, 260\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 46 \, 078 \, 494 \, 212\) | ||||||||||||
\(\ds K_{45}\) | \(=\) | \(\ds 2 \times K_{44} - K_{29}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 46 \, 078 \, 494 \, 212 - 1 \, 406 \, 511\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 92 \, 155 \, 581 \, 913\) | ||||||||||||
\(\ds K_{46}\) | \(=\) | \(\ds 2 \times K_{45} - K_{30}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 92 \, 155 \, 581 \, 913 - 2 \, 813 \, 015\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 184 \, 308 \, 350 \, 811\) | ||||||||||||
\(\ds K_{47}\) | \(=\) | \(\ds 2 \times K_{46} - K_{31}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 184 \, 308 \, 350 \, 811 - 5 \, 625 \, 938\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 368 \, 611 \, 075 \, 684\) | ||||||||||||
\(\ds K_{48}\) | \(=\) | \(\ds 2 \times K_{47} - K_{32}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 368 \, 611 \, 075 \, 684 - 11 \, 251 \, 699\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 737 \, 210 \, 899 \, 669\) | ||||||||||||
\(\ds K_{49}\) | \(=\) | \(\ds 2 \times K_{48} - K_{33}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 737 \, 210 \, 899 \, 669 - 22 \, 503 \, 049\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 1 \, 474 \, 399 \, 296 \, 289\) | ||||||||||||
\(\ds K_{50}\) | \(=\) | \(\ds 2 \times K_{49} - K_{34}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 1 \, 474 \, 399 \, 296 \, 289 - 45 \, 005 \, 404\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \, 948 \, 753 \, 587 \, 174\) | ||||||||||||
\(\ds K_{51}\) | \(=\) | \(\ds 2 \times K_{50} - K_{35}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 2 \, 948 \, 753 \, 587 \, 174 - 90 \, 009 \, 427\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 5 \, 897 \, 417 \, 164 \, 921\) | ||||||||||||
\(\ds K_{52}\) | \(=\) | \(\ds 2 \times K_{51} - K_{36}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 5 \, 897 \, 417 \, 164 \, 921 - 180 \, 016 \, 100\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 11 \, 794 \, 654 \, 313 \, 742\) | ||||||||||||
\(\ds K_{53}\) | \(=\) | \(\ds 2 \times K_{52} - K_{37}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 11 \, 794 \, 654 \, 313 \, 742 - 360 \, 026 \, 700\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 23 \, 588 \, 948 \, 600 \, 784\) | ||||||||||||
\(\ds K_{54}\) | \(=\) | \(\ds 2 \times K_{53} - K_{38}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 23 \, 588 \, 948 \, 600 \, 784 - 720 \, 042 \, 407\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 47 \, 177 \, 177 \, 159 \, 161\) | ||||||||||||
\(\ds K_{55}\) | \(=\) | \(\ds 2 \times K_{54} - K_{39}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 47 \, 177 \, 177 \, 159 \, 161 - 1 \, 440 \, 062 \, 833\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 94 \, 352 \, 914 \, 255 \, 489\) | ||||||||||||
\(\ds K_{56}\) | \(=\) | \(\ds 2 \times K_{55} - K_{40}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 94 \, 352 \, 914 \, 255 \, 489 - 2 \, 880 \, 081 \, 707\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 188 \, 702 \, 948 \, 429 \, 271\) | ||||||||||||
\(\ds K_{57}\) | \(=\) | \(\ds 2 \times K_{56} - K_{41}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 188 \, 702 \, 948 \, 429 \, 271 - 5 \, 760 \, 075 \, 501\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 377 \, 400 \, 136 \, 783 \, 041\) | ||||||||||||
\(\ds K_{58}\) | \(=\) | \(\ds 2 \times K_{57} - K_{42}\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 2 \times 377 \, 400 \, 136 \, 783 \, 041 - 11 \, 519 \, 975 \, 185\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds 754 \, 788 \, 753 \, 590 \, 897\) |
Thus $754 \, 788 \, 753 \, 590 \, 897$ occurs in $K$ and the result follows by definition of Keith number.
$\blacksquare$
Sources
- 1994: K. Shirriff: Computing Replicating Fibonacci Digits (J. Recr. Math. Vol. 26: pp. 191 – 193)
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $754,788,753,590,897$