OFFSET
0,4
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..800
FORMULA
a(0)=a(1)=0, a(2)=1, a(n) = 2*a(n-1)+(n-4)*a(n-2)-(n-4)*a(n-3).
a(n) ~ (sqrt(Pi)+sqrt(2))/2 * n^(n/2-1)*exp(sqrt(n)-n/2-1/4) * (1-17/(24*sqrt(n))). - Vaclav Kotesovec, Dec 27 2012
a(n) = A187044(n-2). - Vaclav Kotesovec, Feb 14 2014
MATHEMATICA
RecurrenceTable[{a[1]==0, a[2]==0, a[n]==a[n-1]+(n-4) a[n-2]+1}, a, {n, 30}]
PROG
(Magma) [n le 2 select 0 else Self(n-1)+(n-4)*Self(n-2) + 1: n in [1..30]];
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Dec 25 2012
STATUS
approved