OFFSET
0,3
COMMENTS
Compare to A007840(n) = Sum_{k=0..n} |Stirling1(n, k)|*k!, which equals the number of factorizations of permutations of n letters into ordered cycles.
For n > 1, a(n) is equal to the permanent of the (n-1) X (n-1) matrix in which the (i, j)-entry is equal to delta(i, j) + i, letting delta denote the Kronecker delta function, as illustrated in the below example. - John M. Campbell, Jan 21 2018
FORMULA
a(n) ~ ((n-1)!)^2. - Vaclav Kotesovec, Sep 30 2014
EXAMPLE
For example, the (5-1) X (5-1) matrix of the form indicated above is equal to
[2 1 1 1]
[2 3 2 2]
[3 3 4 3]
[4 4 4 5]
and the permanent of the above matrix is equal to 957 = a(5). - John M. Campbell, Jan 21 2018
MATHEMATICA
Table[Sum[Abs[StirlingS1[n, k]]*(n-k)!, {k, 0, n}], {n, 0, 20}] (* Vaclav Kotesovec, Sep 30 2014 *)
PROG
(PARI) {Stirling1(n, k)=if(n==0, 1, n!*polcoeff(binomial(x, n), k))}
{a(n)=sum(k=0, n, (-1)^(n-k)*Stirling1(n, k)*(n-k)!)}
for(n=0, 20, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Sep 29 2014
STATUS
approved