OFFSET
0,7
FORMULA
a(0)=1; a(n) = a(n-1) + Sum_{k=2..n-4} a(k)*a(n-4-k).
G.f. A(x) satisfies: A(x) = (1 + x^4 * A(x)^2) / (1 - x + x^4 + x^5). - Ilya Gutkovskiy, Jul 20 2021
MAPLE
A023428 := proc(n)
option remember;
if n = 0 then
1 ;
else
procname(n-1)+add(procname(k)*procname(n-4-k), k=2..n-4) ;
end if;
end proc:
seq(A023428(n), n=0..80) ; # R. J. Mathar, Oct 31 2014
MATHEMATICA
Clear[ a ]; a[ 0 ]=1; a[ n_Integer ] := a[ n ]=a[ n-1 ]+Sum[ a[ k ]*a[ n-4-k ], {k, 2, n-4} ];
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
More terms from Sean A. Irvine, Jun 04 2019
STATUS
approved