OFFSET
1,2
COMMENTS
a(n) = Sum_{k=0..ceiling(n/2)} k*A155517(n,k).
FORMULA
a(2n-1) = n(2n-2)!; a(2n) = 2(2n-2)!*n^2.
EXAMPLE
a(3)=4 because J(123)=2 (counting j=1,2), J(321)=2 (counting j=1,2) and J(132) = J(312) = J(213) = J(231) = 0.
MAPLE
a := proc (n) if `mod`(n, 2) = 1 then (1/2)*(n+1)*factorial(n-1) else (1/2)*factorial(n-2)*n^2 end if end proc: seq(a(n), n = 1 .. 23);
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Jan 26 2009
STATUS
approved