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 A059972 #12 Aug 02 2017 23:55:53 %S A059972 2,3,4,9,30,81,4096,531441,16777216 %N A059972 a(n) is the least positive integer k such that all digits of k are 0 or 1 in exactly n different bases B, where 2 <= B <= k; i.e., such that A068953(k)=n. %C A059972 Is every term except 30 a power of either 2 or 3? %e A059972 For n=4: 9 written in bases 2 through 9 is 1001, 100, 21, 14, 13, 12, 11, 10. In 4 bases, namely 2, 3, 8 and 9, all digits are 0 or 1. %t A059972 f[1]=0; f[k_] := Length[Select[Rest[Union[Divisors[k], Divisors[k-1]]], Max@@IntegerDigits[k, # ]==1&]]; a[n_] := For[k=1, True, k++, If[f[k]==n, Return[k]]] %Y A059972 Cf. A068953. %K A059972 more,base,nonn %O A059972 1,1 %A A059972 _Naohiro Nomoto_, Mar 28 2002 %E A059972 Edited by _Dean Hickerson_, Mar 31 2002