A174193 Expansion of the conjectured generating function for the number of "almost avoiding" permutations in the set Av(321)^{+1}.

1, 1, 2, 6, 23, 103, 488, 2320, 10867, 49971, 225861, 1005821, 4423807, 19255967, 83093364, 355956164, 1515437339, 6417727259, 27054820649, 113602953089, 475370846639, 1983142721039, 8250982614809, 34246497698633, 141838788939623, 586322071478503, 2419474311617803, 9968270142800955, 41010408788528703, 168499207575017087

Offset

0,3

References

R. Brignall et al., Almost avoiding permutations, Discrete Math., 309 (2009),6626-6631.

Links

Table of n, a(n) for n=0..29.

Formula

G.f.: (1-8*x+13*x^2+24*x^3-48*x^4-(1-6*x+x^2+34*x^3-26*x^4-4*x^5)*sqrt(1-4*x))/

(2*x^2*(1 -x)*(1- 4*x)^2)

Conjecture: -(n+2)*(404489*n-1866368)*a(n) +(3147815*n^2-8680082*n-14098754)*a(n-1) +2*(-2336439*n^2+652022*n+14514849)*a(n-2) +8*(-1044770*n^2+10585023*n-20370553)*a(n-3) +8*(642982*n-2004177)*(2*n-9)*a(n-4)=0. - R. J. Mathar, Jun 14 2016

Crossrefs

Cf. A174195.

Sequence in context: A088929 A356111 A279573 * A238639 A226995 A301897

Adjacent sequences: A174190 A174191 A174192 * A174194 A174195 A174196

Keyword

nonn

Author

N. J. A. Sloane, Nov 26 2010

Status

approved