Numbers whose Divisor Sum is Square/Examples/81
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Example of Number whose Divisor Sum is Square
- $\map {\sigma_1} {81} = 121 = 11^2$
Proof
From $\sigma_1$ of $81$:
- $\map {\sigma_1} {81} = 121$
which equals $11^2$.
$\blacksquare$
Sources
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $81$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $81$