OFFSET
1,3
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..200
J. Zeng, The generating function for the difference in even and odd three-line latin rectangles, Ann. Sci. Math. Quebec 20/1 (1996) 105-108. [alternate link]
FORMULA
E.g.f.: x + [(1-x)^2/(1+x)+x/(1+x)^2] * exp(2x). - corrected by Vaclav Kotesovec, Sep 29 2013
a(n) ~ n! * (-1)^(n+1) * n * exp(-2). - Vaclav Kotesovec, Sep 29 2013
MATHEMATICA
Rest[CoefficientList[Series[x + ((1-x)^2/(1+x)+x/(1+x)^2)*E^(2*x), {x, 0, 20}], x]* Range[0, 20]!] (* Vaclav Kotesovec, Sep 29 2013 *)
PROG
(PARI) a(n)=polcoeff(serlaplace(exp(2*x)*((1-x)^2/(1+x)+x/(1+x)^2)), n)
(PARI) a(n)=(-1)^(n-1)*(n-2)*n!/2*polcoeff(Ser(exp(2*(atanh(x)-x))), n)
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Ralf Stephan, Sep 06 2004
STATUS
approved