9999

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Number

$9999$ (nine thousand, nine hundred and ninety-nine) is:

$3^2 \times 11 \times 101$

The $17$th Kaprekar number after $1$, $9$, $45$, $55$, $99$, $297$, $703$, $999$, $2223$, $2728$, $4879$, $4950$, $5050$, $5292$, $7272$, $7777$:

$9999^2 = 99 \, 980 \, 001 \to 9998 + 0001 = 9999$

Also see

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Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $9999$
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $9999$