Largest Pandigital Square
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Theorem
The largest pandigital square (in the sense where pandigital includes the zero) is $9 \, 814 \, 072 \, 356$:
- $9 \, 814 \, 072 \, 356 = 99 \, 066^2$
Proof
We check all the squares of numbers from $99 \, 067$ up to $\floor {\sqrt {9 \, 876 \, 543 \, 210} } = 99 \, 380$, with the following constraints:
Since all these squares has $9$ as its leftmost digit, the number cannot end with $3$ or $7$.
The number cannot end with $0$ since its square will end in $00$.
A pandigital number is divisible by $9$, so our number must be divisible by $3$.
These constraints leaves us with the following $74$ candidates:
\(\ds 99 \, 069^2\) | \(=\) | \(\ds 9 \, 814 \, 666 \, 761\) | ||||||||||||
\(\ds 99 \, 072^2\) | \(=\) | \(\ds 9 \, 815 \, 261 \, 184\) | ||||||||||||
\(\ds 99 \, 075^2\) | \(=\) | \(\ds 9 \, 815 \, 855 \, 625\) | ||||||||||||
\(\ds 99 \, 078^2\) | \(=\) | \(\ds 9 \, 816 \, 450 \, 084\) | ||||||||||||
\(\ds 99 \, 081^2\) | \(=\) | \(\ds 9 \, 817 \, 044 \, 561\) | ||||||||||||
\(\ds 99 \, 084^2\) | \(=\) | \(\ds 9 \, 817 \, 639 \, 056\) | ||||||||||||
\(\ds 99 \, 096^2\) | \(=\) | \(\ds 9 \, 820 \, 017 \, 216\) | ||||||||||||
\(\ds 99 \, 099^2\) | \(=\) | \(\ds 9 \, 820 \, 611 \, 801\) | ||||||||||||
\(\ds 99 \, 102^2\) | \(=\) | \(\ds 9 \, 821 \, 206 \, 404\) | ||||||||||||
\(\ds 99 \, 105^2\) | \(=\) | \(\ds 9 \, 821 \, 801 \, 025\) | ||||||||||||
\(\ds 99 \, 108^2\) | \(=\) | \(\ds 9 \, 822 \, 395 \, 664\) | ||||||||||||
\(\ds 99 \, 111^2\) | \(=\) | \(\ds 9 \, 822 \, 990 \, 321\) | ||||||||||||
\(\ds 99 \, 114^2\) | \(=\) | \(\ds 9 \, 823 \, 584 \, 996\) | ||||||||||||
\(\ds 99 \, 126^2\) | \(=\) | \(\ds 9 \, 825 \, 963 \, 876\) | ||||||||||||
\(\ds 99 \, 129^2\) | \(=\) | \(\ds 9 \, 826 \, 558 \, 641\) | ||||||||||||
\(\ds 99 \, 132^2\) | \(=\) | \(\ds 9 \, 827 \, 153 \, 424\) | ||||||||||||
\(\ds 99 \, 135^2\) | \(=\) | \(\ds 9 \, 827 \, 748 \, 225\) | ||||||||||||
\(\ds 99 \, 138^2\) | \(=\) | \(\ds 9 \, 828 \, 343 \, 044\) | ||||||||||||
\(\ds 99 \, 141^2\) | \(=\) | \(\ds 9 \, 828 \, 937 \, 881\) | ||||||||||||
\(\ds 99 \, 144^2\) | \(=\) | \(\ds 9 \, 829 \, 532 \, 736\) | ||||||||||||
\(\ds 99 \, 156^2\) | \(=\) | \(\ds 9 \, 831 \, 912 \, 336\) | ||||||||||||
\(\ds 99 \, 159^2\) | \(=\) | \(\ds 9 \, 832 \, 507 \, 281\) | ||||||||||||
\(\ds 99 \, 162^2\) | \(=\) | \(\ds 9 \, 833 \, 102 \, 244\) | ||||||||||||
\(\ds 99 \, 165^2\) | \(=\) | \(\ds 9 \, 833 \, 697 \, 225\) | ||||||||||||
\(\ds 99 \, 168^2\) | \(=\) | \(\ds 9 \, 834 \, 292 \, 224\) | ||||||||||||
\(\ds 99 \, 171^2\) | \(=\) | \(\ds 9 \, 834 \, 887 \, 241\) | ||||||||||||
\(\ds 99 \, 174^2\) | \(=\) | \(\ds 9 \, 835 \, 482 \, 276\) | ||||||||||||
\(\ds 99 \, 186^2\) | \(=\) | \(\ds 9 \, 837 \, 862 \, 596\) | ||||||||||||
\(\ds 99 \, 189^2\) | \(=\) | \(\ds 9 \, 838 \, 457 \, 721\) | ||||||||||||
\(\ds 99 \, 192^2\) | \(=\) | \(\ds 9 \, 839 \, 052 \, 864\) | ||||||||||||
\(\ds 99 \, 195^2\) | \(=\) | \(\ds 9 \, 839 \, 648 \, 025\) | ||||||||||||
\(\ds 99 \, 198^2\) | \(=\) | \(\ds 9 \, 840 \, 243 \, 204\) | ||||||||||||
\(\ds 99 \, 201^2\) | \(=\) | \(\ds 9 \, 840 \, 838 \, 401\) | ||||||||||||
\(\ds 99 \, 204^2\) | \(=\) | \(\ds 9 \, 841 \, 433 \, 616\) | ||||||||||||
\(\ds 99 \, 216^2\) | \(=\) | \(\ds 9 \, 843 \, 814 \, 656\) | ||||||||||||
\(\ds 99 \, 219^2\) | \(=\) | \(\ds 9 \, 844 \, 409 \, 961\) | ||||||||||||
\(\ds 99 \, 222^2\) | \(=\) | \(\ds 9 \, 845 \, 005 \, 284\) | ||||||||||||
\(\ds 99 \, 225^2\) | \(=\) | \(\ds 9 \, 845 \, 600 \, 625\) | ||||||||||||
\(\ds 99 \, 228^2\) | \(=\) | \(\ds 9 \, 846 \, 195 \, 984\) | ||||||||||||
\(\ds 99 \, 231^2\) | \(=\) | \(\ds 9 \, 846 \, 791 \, 361\) | ||||||||||||
\(\ds 99 \, 234^2\) | \(=\) | \(\ds 9 \, 847 \, 386 \, 756\) | ||||||||||||
\(\ds 99 \, 246^2\) | \(=\) | \(\ds 9 \, 849 \, 768 \, 516\) | ||||||||||||
\(\ds 99 \, 249^2\) | \(=\) | \(\ds 9 \, 850 \, 364 \, 001\) | ||||||||||||
\(\ds 99 \, 252^2\) | \(=\) | \(\ds 9 \, 850 \, 959 \, 504\) | ||||||||||||
\(\ds 99 \, 255^2\) | \(=\) | \(\ds 9 \, 851 \, 555 \, 025\) | ||||||||||||
\(\ds 99 \, 258^2\) | \(=\) | \(\ds 9 \, 852 \, 150 \, 564\) | ||||||||||||
\(\ds 99 \, 261^2\) | \(=\) | \(\ds 9 \, 852 \, 746 \, 121\) | ||||||||||||
\(\ds 99 \, 264^2\) | \(=\) | \(\ds 9 \, 853 \, 341 \, 696\) | ||||||||||||
\(\ds 99 \, 276^2\) | \(=\) | \(\ds 9 \, 855 \, 724 \, 176\) | ||||||||||||
\(\ds 99 \, 279^2\) | \(=\) | \(\ds 9 \, 856 \, 319 \, 841\) | ||||||||||||
\(\ds 99 \, 282^2\) | \(=\) | \(\ds 9 \, 856 \, 915 \, 524\) | ||||||||||||
\(\ds 99 \, 285^2\) | \(=\) | \(\ds 9 \, 857 \, 511 \, 225\) | ||||||||||||
\(\ds 99 \, 288^2\) | \(=\) | \(\ds 9 \, 858 \, 106 \, 944\) | ||||||||||||
\(\ds 99 \, 291^2\) | \(=\) | \(\ds 9 \, 858 \, 702 \, 681\) | ||||||||||||
\(\ds 99 \, 294^2\) | \(=\) | \(\ds 9 \, 859 \, 298 \, 436\) | ||||||||||||
\(\ds 99 \, 306^2\) | \(=\) | \(\ds 9 \, 861 \, 681 \, 636\) | ||||||||||||
\(\ds 99 \, 309^2\) | \(=\) | \(\ds 9 \, 862 \, 277 \, 481\) | ||||||||||||
\(\ds 99 \, 312^2\) | \(=\) | \(\ds 9 \, 862 \, 873 \, 344\) | ||||||||||||
\(\ds 99 \, 315^2\) | \(=\) | \(\ds 9 \, 863 \, 469 \, 225\) | ||||||||||||
\(\ds 99 \, 318^2\) | \(=\) | \(\ds 9 \, 864 \, 065 \, 124\) | ||||||||||||
\(\ds 99 \, 321^2\) | \(=\) | \(\ds 9 \, 864 \, 661 \, 041\) | ||||||||||||
\(\ds 99 \, 324^2\) | \(=\) | \(\ds 9 \, 865 \, 256 \, 976\) | ||||||||||||
\(\ds 99 \, 336^2\) | \(=\) | \(\ds 9 \, 867 \, 640 \, 896\) | ||||||||||||
\(\ds 99 \, 339^2\) | \(=\) | \(\ds 9 \, 868 \, 236 \, 921\) | ||||||||||||
\(\ds 99 \, 342^2\) | \(=\) | \(\ds 9 \, 868 \, 832 \, 964\) | ||||||||||||
\(\ds 99 \, 345^2\) | \(=\) | \(\ds 9 \, 869 \, 429 \, 025\) | ||||||||||||
\(\ds 99 \, 348^2\) | \(=\) | \(\ds 9 \, 870 \, 025 \, 104\) | ||||||||||||
\(\ds 99 \, 351^2\) | \(=\) | \(\ds 9 \, 870 \, 621 \, 201\) | ||||||||||||
\(\ds 99 \, 354^2\) | \(=\) | \(\ds 9 \, 871 \, 217 \, 316\) | ||||||||||||
\(\ds 99 \, 366^2\) | \(=\) | \(\ds 9 \, 873 \, 601 \, 956\) | ||||||||||||
\(\ds 99 \, 369^2\) | \(=\) | \(\ds 9 \, 874 \, 198 \, 161\) | ||||||||||||
\(\ds 99 \, 372^2\) | \(=\) | \(\ds 9 \, 874 \, 794 \, 384\) | ||||||||||||
\(\ds 99 \, 375^2\) | \(=\) | \(\ds 9 \, 875 \, 390 \, 625\) | ||||||||||||
\(\ds 99 \, 378^2\) | \(=\) | \(\ds 9 \, 875 \, 986 \, 884\) |
By inspection, none of these numbers are pandigital.
$\blacksquare$
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $9,814,072,356$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $9,814,072,356$