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 A136113 #8 Mar 31 2012 13:48:25 %S A136113 1,5,12,35,51,92,117,176,330,477,782,852,1080,3876,4347,7526,7740, %T A136113 9801,13776,14652,22632,24512,27270,39285,69876,85562,88452,103622, %U A136113 124272,137562,144926,193142,220992,268182,315792,343922,354051,403782,523626 %N A136113 Pentagonal numbers > 0 which are not the difference of two larger pentagonal numbers. %H A136113 Donovan Johnson, <a href="/A136113/b136113.txt">Table of n, a(n) for n = 1..500</a> %F A136113 a(n)=A000326(A136112(n)). A number m is in this sequence iff A136114(m) = 0 iff A136115(m) = 0. %e A136113 a(1..3)=P(1),P(2),P(3) since these cannot be written as difference of 2 other pentagonal numbers > 0. %e A136113 P(4)=22=P(8)-P(7), therefore P(4) is not in this sequence. %o A136113 (PARI) P(n)=n*(3*n-1)>>1 /* a.k.a. A000326 */ %o A136113 isPent(t)=P(sqrtint((t<<1)\3)+1)==t %o A136113 for( i=1,999,for( j=i+1,(P(i)-1)\3, isPent(P(i)+P(j))&next(2)); print1(P(i)",")) %Y A136113 Cf. A000326, A136112-A136118. %K A136113 nonn %O A136113 1,2 %A A136113 _M. F. Hasler_, Dec 15 2007, Feb 07 2008 %E A136113 a(34)-a(39) from _Donovan Johnson_, Sep 05 2008