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 A213780 #13 Feb 18 2024 07:58:27 %S A213780 1,6,17,40,78,140,230,360,535,770,1071,1456,1932,2520,3228,4080,5085, %T A213780 6270,7645,9240,11066,13156,15522,18200,21203,24570,28315,32480,37080, %U A213780 42160,47736,53856,60537,67830,75753,84360,93670,103740,114590 %N A213780 Antidiagonal sums of the convolution array A213778. %H A213780 Clark Kimberling, <a href="/A213780/b213780.txt">Table of n, a(n) for n = 1..1000</a> %H A213780 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (3,-1,-5,5,1,-3,1). %F A213780 a(n) = 3*a(n-1) - a(n-2) - 5*a(n-3) + 5*a(n-4) + a(n-5) - 3*a(n-6) + a(n-7). %F A213780 G.f.: f(x)/g(x), where f(x) = x*(1 + 3*x) and g(x) = (1 + x)^2 *(1 - x)^5. %t A213780 (See A213778.) %Y A213780 Cf. A213778, A213500. %K A213780 nonn,easy %O A213780 1,2 %A A213780 _Clark Kimberling_, Jun 21 2012