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 A107869 #11 Dec 07 2019 12:18:24 %S A107869 1,3,15,120,1365,20349,376740,8347680,215553195,6358402050, %T A107869 210980549208,7778680504140,315502265971620,13961746143269400, %U A107869 669413654240461560,34569147570568156800,1912924003884628655655,112923282067713332728110 %N A107869 Column 1 of triangle A107867; a(n) = binomial( n*(n+1)/2 + n+1, n). %o A107869 (PARI) a(n)=binomial(n*(n+1)/2+n+1,n) %o A107869 (Sage) [binomial(binomial(binomial(n+1,n),n-1),n-1) for n in range(1, 19)] # _Zerinvary Lajos_, Nov 30 2009 %Y A107869 Cf. A107867, A107868. %K A107869 nonn %O A107869 0,2 %A A107869 _Paul D. Hanna_, Jun 04 2005