OFFSET
0,3
LINKS
A. Bernini, F. Disanto, R. Pinzani and S. Rinaldi, Permutations defining convex permutominoes, J. Int. Seq. 10 (2007) # 07.9.7. [See C^{~}_{n}.]
Filippo Disanto, Andrea Frosini and Simone Rinaldi, Renzo Pinzani, The Combinatorics of Convex Permutominoes, Southeast Asian Bulletin of Mathematics (2008) 32: 883-912.
F. Disanto and S. Rinaldi, Symmetric convex permutominoes and involutions, PU. M. A., Vol. 22 (2011), No. 1, pp. 39-60.
I. Fanti, A. Frosini, E. Grazzini, R. Pinzani and S. Rinaldi, Characterization and enumeration of some classes of permutominoes, PU. M. A., Vol. 18 (2007), No. 3-4, pp. 265-290.
FORMULA
Conjecture: n*(4*n^2-21*n+19)*a(n) +2*(-16*n^3+80*n^2-77*n+3)*a(n-1) +8*(2*n-3)*(4*n^2-13*n+2)*a(n-2)=0. - R. J. Mathar, Jan 04 2017
Conjecture: n*a(n) +2*(-4*n-1)*a(n-1) +72*a(n-2) +32*(4*n-15)*a(n-3) +128*(-2*n+7)*a(n-4)=0. - R. J. Mathar, Jan 04 2017
PROG
(PARI) a(n) = if (n==0, 1, 2*(n+2)*4^(n-2)-(n/4)*((3-4*n)/(1-2*n))*binomial(2*n, n)); \\ Michel Marcus, Nov 02 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 28 2007
EXTENSIONS
Missing a(0) inserted by Michel Marcus, Jun 13 2022
STATUS
approved