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 A258216 #11 May 25 2015 19:41:56
%S A258216 1,1,2,6,24,120,480,3600,30240,151200,1693440,20321280,121927680,
%T A258216 1828915200,28740096000,201180672000,3793692672000,73977007104000,
%U A258216 591816056832000,13463815292928000,314155690168320000
%N A258216 Number of permutations of {1,2,3,...,n} such that no multiples of 3 are adjacent.
%F A258216 a(n) = factorial(n-floor(n/3))*fallfac(n+1-floor(n/3),floor(n/3)), where fallfac is falling factorial, A008279.
%F A258216 a(n) ~ n! * 2^(2*n+2-2*floor(n,3)/3) / 3^(n+1/2). - _Vaclav Kotesovec_, May 23 2015
%t A258216 Table[Factorial[n-Floor[n/3]]*FactorialPower[n+1-Floor[n/3],Floor[n/3],1], {n, 0, 20}]
%Y A258216 Cf. A008279, A010790, A258213.
%K A258216 nonn,easy
%O A258216 0,3
%A A258216 _Ran Pan_, May 23 2015