A182555 Expansion of g.f. (3-4*x-sqrt(1-4*x^2))/(2*(1-2*x)^2).

1, 2, 5, 12, 29, 68, 158, 360, 813, 1812, 4010, 8792, 19170, 41512, 89500, 191952, 410237, 873140, 1853042, 3919608, 8271126, 17406072, 36556580, 76602032, 160240594, 334554248, 697462628, 1451633520, 3017426468, 6263171792, 12985655736, 26889935776, 55626815005, 114947516916, 237318165314, 489482593592, 1008787357902, 2077219057240, 4274204436052

Offset: 0

Author

N. J. A. Sloane, May 05 2012

Keywords

• nonn

Links

• F. Disanto and S. Rinaldi, Symmetric convex permutominoes and involutions, PU. M. A., Vol. 22 (2011), No. 1, pp. 39-60; See M_n.

Formula

G.f.: (3-4*x-sqrt(1-4*x^2))/(2*(1-2*x)^2).

D-finite with recurrence: n*(n-4)*a(n) +2*(5+2n-n^2)*a(n-1) -4*(n-2)*(n-5)*a(n-2) +8*(n-2)*(n-3)*a(n-3)=0. - R. J. Mathar, Jun 28 2012

a(n) ~ n*2^(n-1) * (1-2*sqrt(2/Pi)/sqrt(n)). - Vaclav Kotesovec, Jun 29 2013