A007753 a(n) = Sum_{k=0..n-1} binomial(a(k)^2, k).

1, 1, 2, 8, 41672, 378916495683075745757412513402693048

Offset

0,3

Links

G. C. Greubel, Table of n, a(n) for n = 0..6

Maple

a:= proc(n) option remember;
   if n=0 then 1
   else add(binomial(a(j)^2, j), j=0..n-1)
   fi; end:
seq(a(n), n=0..6); # G. C. Greubel, Mar 04 2020

Mathematica

a[n_]:= a[n]= If[n==0, 1, Sum[Binomial[a[j]^2, j], {j, 0, n-1}] ]; Table[a[n], {n, 0, 6}] (* G. C. Greubel, Mar 04 2020 *)

Prog

(Sage)
@CachedFunction
def a(n):
    if (n==0): return 1
    else: return sum(binomial(a(j)^2, j) for j in (0..n-1))
[a(n) for n in (0..6)] # G. C. Greubel, Mar 04 2020

Crossrefs

Sequence in context: A058437 A185681 A046967 * A272331 A256065 A081979

Adjacent sequences: A007750 A007751 A007752 * A007754 A007755 A007756

Keyword

easy,nonn

Author

Barry Brunson (bbrunson(AT)wku.edu)

Status

approved