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 A215108 #7 Jun 02 2025 08:06:19 %S A215108 0,1,4,8,17,35,66,124,229,414,742,1318,2320,4059,7062,12224,21071, %T A215108 36185,61930,105678,179847,305326,517212,874380,1475472,2485573, %U A215108 4180648,7021544,11777117,19728911,33011202 %N A215108 a(n) = A215082(2*n). %F A215108 a(n) = a(n-1) + 2*a(n-2) + a(n-3) - 2*a(n-4) - 3*a(n-5) -a(n-6), a(0) = 0, a(1) = 1, a(2) = 4, a(3) = 8, a(4) = 17, a(5) = 35 . %F A215108 G.f.: x*(x+1)*(2x+1)/((x^2+x+1)*(x^2+x-1)^2) %Y A215108 Cf. A000045, A023607 %K A215108 nonn,easy %O A215108 0,3 %A A215108 _Philippe Deléham_, Aug 03 2012