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 A261799 #13 Aug 06 2024 09:56:37
%S A261799 1,7,77,819,8687,92141,977347,10366833,109962202,1166381804,
%T A261799 12371946734,131230670312,1391978902090,14764881252772,
%U A261799 156612803600094,1661210126351328,17620647995924820,186904251828901124,1982515022137687464,21028766197355391048
%N A261799 Number of 7-compositions of n: matrices with 7 rows of nonnegative integers with positive column sums and total element sum n.
%C A261799 Also the number of compositions of n where each part i is marked with a word of length i over a septenary alphabet whose letters appear in alphabetical order.
%H A261799 Alois P. Heinz, <a href="/A261799/b261799.txt">Table of n, a(n) for n = 0..975</a>
%H A261799 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (14,-42,70,-70,42,-14,2).
%F A261799 G.f.: (1-x)^7/(2*(1-x)^7-1).
%F A261799 a(n) = A261780(n,7).
%F A261799 a(n) = Sum_{k>=0} (1/2)^(k+1) * binomial(n-1+7*k,n). - _Seiichi Manyama_, Aug 06 2024
%p A261799 a:= proc(n) option remember; `if`(n=0, 1,
%p A261799 add(a(n-j)*binomial(j+6, 6), j=1..n))
%p A261799 end:
%p A261799 seq(a(n), n=0..20);
%Y A261799 Column k=7 of A261780.
%K A261799 nonn,easy
%O A261799 0,2
%A A261799 _Alois P. Heinz_, Sep 01 2015