OFFSET
0,4
MAPLE
spec := [ S, {N=Union(Z, S, P, Q), S=Set(Union(Z, P, Q), card>=2), P=Set(Union(Z, S, Q), card>=2), Q=Set(Union(Z, S, P), card>=2)} ]; [seq(combstruct[count](spec, size=n), n=0..40)]; # N=A058540, S=A058371
spec:=[S, {S=Set(Union(Z, S, S), card>=2)}]; [seq(combstruct[count](spec, size=n), n=0..25)]; # Vladeta Jovovic, Jun 25 2007
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Dec 26 2000
STATUS
approved