This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A033618 #13 Jul 06 2024 11:54:31 %S A033618 2,2,2,2,3,2,2,3,2,3,3,2,4,5,2,3,3,4,3,4,3,4,5,3,3,3,3,2,3,3,3,6,3,2, %T A033618 3,2,3,3,3,3,4,2,3,3,7,3,4,3,4,5,4,3,4,2,2,3,3,3,4,3,3,3,3,4,3,2,3,6, %U A033618 2,3,3 %N A033618 Number of ways n-th repdigit number, A010785(n), can be expressed as a polygonal number. %H A033618 M. Keith, <a href="http://www.cs.uwaterloo.ca/journals/JIS/keith.html">On Repdigit Polygonal Numbers</a>, J. Integer Sequences, Vol. 1, 1998, #6. %e A033618 The n-th k-sided polygonal number is P(n,k)=n((k-2)n+4-k)/2 (k >= 2, n >= 1). For each repdigit number R>=2, sequence gives number of (n,k) such that P(n,k)=R. %K A033618 nonn,base %O A033618 2,1 %A A033618 _Mike Keith_