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A220899 Number of 2-face-free maps on n edges. 0
0, 2, 6, 23, 90, 372, 1594, 7042, 31888, 147402, 693298, 3309625, 16003002, 78248534, 386383508, 1924611467, 9661445944, 48839412404, 248446494564, 1271087170022, 6536984366596, 33779007662386, 175313286917450, 913549922063711, 4778230471883676, 25078497357291840, 132047498330780864, 697362268720301802 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

LINKS

Table of n, a(n) for n=2..29.

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

Sequence in context: A150280 A303071 A150281 * A150282 A150283 A150284

Adjacent sequences:  A220896 A220897 A220898 * A220900 A220901 A220902

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Jan 01 2013

STATUS

approved

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Last modified October 18 08:10 EDT 2021. Contains 348066 sequences. (Running on oeis4.)