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 A173470 #3 Mar 31 2012 12:38:28
%S A173470 85,781,137257,28531167061
%N A173470 Semiprimes in A023037.
%C A173470 The terms a(5) etc. have at least 63 digits (if they exist), so the pattern of terms does not continue as in A001039. [From _R. J. Mathar_, Feb 27 2010]
%t A173470 f1[n_]:=Module[{s=0},Do[s+=n^a,{a,0,n-1}];s]; f2[n_]:=Last/@FactorInteger[n]=={1,1}||Last/@FactorInteger[n]=={2}; Select[Table[f1[n],{n,50}],f2[ # ]&]
%K A173470 nonn
%O A173470 1,1
%A A173470 _Vladimir Joseph Stephan Orlovsky_, Feb 19 2010