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 A172425 #13 Apr 25 2016 11:45:30 %S A172425 37926,279046,2514726,34797726,71254566,348145726,566225926,606245926, %T A172425 828497488,1206646551,8750871976,11481404326,21078151200,28120290876, %U A172425 62963640936,75128827176,77009692800,96868002726,120282238710,147061923750,165998399400,297022824126,325443925926,416397477888 %N A172425 Pentagonal pyramidal numbers which are the sum of two other such numbers: A002411(k) = A002411(i)+A002411(j) with i,j>0. %C A172425 The corresponding indices are listed in A172437. This answers a question posed in A133459. %H A172425 Donovan Johnson, <a href="/A172425/b172425.txt">Table of n, a(n) for n = 1..160</a> %F A172425 a(n) = A002411(A172437(n)) %o A172425 (PARI) for(n=1,99999, for(m=1,n-1, isA002411(A002411(n)-A002411(m)) | next; print1(A002411(n)", "); break)) /* needs A002411() and isA240011() */ %Y A172425 Cf. A133459, A172437. %K A172425 nonn %O A172425 1,1 %A A172425 _M. F. Hasler_, Nov 20 2010