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 A211231 #5 Apr 09 2012 18:38:41 %S A211231 1,3,6,10,27,33,108,108,405,351,1458,1134,5103,3645,17496,11664,59049, %T A211231 37179,196830,118098,649539,373977,2125764,1180980,6908733,3720087, %U A211231 22320522,11691702,71744535 %N A211231 Row sums of A211230. %F A211231 a(2*n) = (n+1)*3^n; a(2*n+1) = (n+9)*3^(n-1). %F A211231 O.g.f.: (1+3*x-8*x^3)/(1-3*x^2)^2 = 1 + 3*x + 6*x^2 + 10*x^3 + .... %Y A211231 Cf. A211227, A211230. %K A211231 nonn,easy %O A211231 0,2 %A A211231 _Peter Bala_, Apr 05 2012