OFFSET
2,2
LINKS
S. Kitaev, P. Salimov, C. Severs and H. Ulfarsson, Restricted non-separable planar maps and some pattern avoiding permutations, preprint 2012.
S. Kitaev, P. Salimov, C. Severs and H. Ulfarsson, Restricted non-separable planar maps and some pattern avoiding permutations, Discrete Applied Mathematics, Volume 161, Issues 16-17, November 2013, Pages 2514-2526.
FORMULA
G.f. = P(x) - xP(x), where P(x) = g.f. for A220898 (also P(x) = A(x/(1+x)), where A(x) = g.f. for A000139).
Conjecture: 2*(n+1)*(2*n+1)*a(n) +(-23*n^2+31*n-6)*a(n-1) +2*(-4*n^2-9*n+25)*a(n-2) +2*(23*n^2-142*n+174)*a(n-3) +4*(n+8)*(n-5)*a(n-4) -23*(n-5)*(n-6)*a(n-5)=0. - R. J. Mathar, Jul 17 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jan 01 2013
STATUS
approved