OFFSET
0,2
COMMENTS
Also unsigned second column of triangle A136657 divided by 2.
REFERENCES
Ch. A. Charalambides, Enumerative Combinatorics, Chapman & Hall/CRC, Boca Raton, Florida, 2002, Table 8.3, p. 311, with s=-2, k=2 column/4.
FORMULA
a(n) = |A136656(n+2,2)|/4, n>=0.
E.g.f.: (2+6*x-3*x^2)/(2*(1-x)^6) (derived from the one given for the column k=2 under A136656)
a(n) = (n+4)!/2 * sum((k+1)!/(k+4)!,k=1..n), with offset 1. [Gary Detlefs, Jul 27 2010]
a(n) = (1/48) * (n+8)*(n+1)*(n+3)!. [Gary Detlefs, Aug 03 2010]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Feb 22 2008
STATUS
approved