Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #18 Aug 03 2022 17:46:54
%S 1,1,13,461,29093,2829325,392743957,73943424413,18176728317413,
%T 5661698774848621,2181096921557783605,1018705098450570562877,
%U 567347013156626397484421,371514945708955154128328461,282629242654284555347577144277,247210800978211588125067686948317
%N Bisection of A003319: a(n) = A003319(2n).
%H Michael De Vlieger, <a href="/A272656/b272656.txt">Table of n, a(n) for n = 0..224</a> (a(n) for n = 1..200 from Vincenzo Librandi)
%t (* b = A003319 *) b[n_] := b[n] = n! - Sum[k!*b[n-k], {k, 1, n-1} ]; a[n_] := b[2 n]; Table[a[n], {n, 0, 15}] (* _Jean-François Alcover_, Feb 18 2018 *)
%Y Cf. A003319, A272657.
%K nonn
%O 0,3
%A _N. J. A. Sloane_, May 15 2016
%E a(0) = 1 set by _Peter Luschny_, Aug 03 2022