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 A277421 #13 Feb 16 2025 08:33:36
%S A277421 1,8,254,13614,1025048,99368620,11781698256,1651548277946,
%T A277421 267197019684224,49000715036948304,10044513851042988800,
%U A277421 2275926588768085912582,564838094735322988575744,152378369304839730672573044,44397985962782115253758973952
%N A277421 a(n) = n!*LaguerreL(n, -7*n).
%H A277421 G. C. Greubel, <a href="/A277421/b277421.txt">Table of n, a(n) for n = 0..250</a>
%H A277421 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/LaguerrePolynomial.html">Laguerre Polynomial</a>
%H A277421 Wikipedia, <a href="https://en.wikipedia.org/wiki/Laguerre_polynomials">Laguerre polynomials</a>
%F A277421 a(n) = n! * Sum_{k=0..n} binomial(n, k) * 7^k * n^k / k!.
%F A277421 a(n) ~ sqrt(1/2 + 9/(2*sqrt(77))) * ((9 + sqrt(77))/2)^n * exp((-9 + sqrt(77))*n/2) * n^n.
%t A277421 Table[n!*LaguerreL[n, -7*n], {n, 0, 20}]
%t A277421 Flatten[{1, Table[n!*Sum[Binomial[n, k] * 7^k * n^k / k!, {k, 0, n}], {n, 1, 20}]}]
%o A277421 (PARI) for(n=0, 30, print1(n!*sum(k=0, n, binomial(n,k)*7^k*n^k/k!), ", ")) \\ _G. C. Greubel_, May 15 2018
%o A277421 (Magma) [Factorial(n)*(&+[Binomial(n,k)*7^k*n^k/Factorial(k): k in [0..n]]): n in [0..30]]; // _G. C. Greubel_, May 15 2018
%Y A277421 Cf. A277373, A277391, A277392, A277418, A277419, A277420, A277422.
%Y A277421 Cf. A002720, A087912, A277382.
%K A277421 nonn
%O A277421 0,2
%A A277421 _Vaclav Kotesovec_, Oct 14 2016