

A054392


Number of permutations with certain forbidden subsequences.


2



1, 1, 2, 5, 14, 42, 131, 418, 1352, 4410, 14463, 47605, 157084, 519255, 1718653, 5693903, 18877509, 62620857, 207816230, 689899944, 2290913666, 7608939443, 25276349558, 83977959853, 279039638062, 927272169336, 3081641953082
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OFFSET

0,3


COMMENTS

Apparently the Motzkin transform of A005251, after A005251(0) is set to 1. [From R. J. Mathar, Dec 11 2008]


LINKS

Table of n, a(n) for n=0..26.
E. Barcucci et al., From Motzkin to Catalan Permutations, Discr. Math., 217 (2000), 3349.


EXAMPLE

G.f. = 1 + x + 2*x^2 + 5*x^3 + 14*x^4 + 42*x^5 + 131*x^6 + 418*x^7 + 1352*x^8 + ...


PROG

(PARI) {a(n) = if( n<1, n==0, polcoeff( subst( x * (1  x) / (1  2*x + x^2  x^3), x, serreverse( x / (1 + x + x^2) + x * O(x^n))), n))}; /* Michael Somos, Aug 06 2014 */


CROSSREFS

Interpolates between Motzkin numbers (A001006) and Catalan numbers (A000108). Cf. A005773, A054391A054394.
Sequence in context: A148328 A080937 A196417 * A006930 A036767 A061922
Adjacent sequences: A054389 A054390 A054391 * A054393 A054394 A054395


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Elisa Pergola (elisa(AT)dsi.unifi.it), May 21 2000


STATUS

approved



