OFFSET
8,2
COMMENTS
Number of permutations of length n with exactly four valleys.
LINKS
Désiré André, Mémoire sur les séquences des permutations circulaires, Bulletin de la S. M. F., tome 23 (1895), pp. 122-184.
R. G. Rieper and M. Zeleke, Valleyless Sequences, arXiv:math/0005180 [math.CO], 2000.
FORMULA
G.f.: 256*x^9*(31 - 788*x + 8096*x^2 - 43132*x^3 + 126072*x^4 - 192672*x^5 + 120960*x^6)/ ((1-2*x)^5*(1-4*x)^4*(1-6*x)^3*(1-8*x)^2*(1-10*x)). - Ray Chandler, Dec 06 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jul 25 2010
EXTENSIONS
More terms from Ray Chandler, Dec 06 2011
STATUS
approved