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 A249349 #14 Oct 28 2014 05:19:25 %S A249349 0,1,7,52,472,5197,67567,1013512,17229712,327364537,6874655287, %T A249349 158117071612,3952926790312,106729023338437,3095141676814687, %U A249349 95949391981255312,3166329935381425312,110821547738349885937,4100397266318945779687,159915493386438885407812 %N A249349 (A001147(n+1)-1)/2, equals the index of A249348(n) within the triangular numbers A000217. %C A249349 Also a(n) = floor(sqrt(A249348(n)*2)). %C A249349 The positive terms are of the form 3k-2; this k (= 1, 3, 18, 157, ...) is the index of A249348(n) within the centered 9-gonal numbers A060544. %F A249349 a(n) +(-2*n-3)*a(n-1) +(4*n-1)*a(n-2) +(-2*n+3)*a(n-3)=0. - _R. J. Mathar_, Oct 28 2014 %o A249349 (PARI) a(n)=A001147(n+1)\2 %o A249349 (PARI) vector(10,n,A001147(n)\2) \\ To get the initial term a(0) for n=1. %K A249349 nonn %O A249349 0,3 %A A249349 _M. F. Hasler_, Oct 26 2014