OFFSET
0,3
LINKS
Harvey P. Dale, Table of n, a(n) for n = 0..417
Tomislav Doslic and R. Sharafdini, Hosoya Index of Splices, Bridges, and Necklaces, in Distance, Symmetry, and Topology in Carbon Nanomaterials, 2016, pp 147-156. Part of the Carbon Materials: Chemistry and Physics book series (CMCP, volume 9), doi:10.1007/978-3-319-31584-3_10. See the end of Section 2 (page 9).
MAPLE
f:=proc(n) option remember;
if n <= 1 then 1 elif n=2 then 3 else
n*f(n-1)+(n-1)*(n-2)*f(n-2); fi; end;
[seq(f(n), n=0..20)];
MATHEMATICA
nxt[{n_, a_, b_}]:={n+1, b, b(n+1)+n(n-1)a}; Join[{1}, NestList[nxt, {2, 1, 3}, 20][[;; , 2]]] (* Harvey P. Dale, Jan 20 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Aug 27 2017
STATUS
approved