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 #3 Mar 03 2023 23:35:11
%S 0,1,1,3,20,9731608032706560018
%N a(0)=0, a(1)=1; thereafter a(n) = (n-1)*a(n-1)! + (n-2)*a(n-2)!.
%C The next term is too large to include.
%C There is a suggestion that this is mentioned in Kenneth H. Rosen's book "Discrete Mathematics and Its Applications". It would be nice to have a precise reference, including edition, date, and page number.
%Y Cf. A000045, A005604, A114045.
%K nonn
%O 0,4
%A _N. J. A. Sloane_, Mar 03 2023, following a suggestion from _Akshat Kadia_, Feb 2023