info prev up next book cdrom email home

Sum-Product Number

A sum-product number is a number $n$ such that the sum of $n$'s digits times the product of $n$'s digit is $n$ itself, for example

\begin{displaymath}
135=(1+3+5)(1\cdot 3\cdot 5).
\end{displaymath}

The only sum-product numbers less than $10^7$ are 1, 135, and 144.

See also Amenable Number




© 1996-9 Eric W. Weisstein
1999-05-26