A335026 - OEIS

%I #4 May 20 2020 05:40:30

%S 0,9,9,234,558,12024,47736,1021680,5795280,129418560,963938880,

%T 22835675520,211767696000,5349794688000,59562324864000,

%U 1605652989696000,20903846245632000,600544575525888000,8962083073778688000,273802240880695296000,4611450448589580288000

%N a(n) = (n + 1)^2*a(n - 2) + a(n - 1), starting 0, 9, ....

%p a := proc(n) option remember; if n < 3 then return [0, 9][n] fi;

%p (n + 1)^2*a(n - 2) + a(n - 1) end: print(seq(a(n), n=1..21));

%K nonn

%O 1,2

%A _Peter Luschny_, May 20 2020