|
|
A358494
|
|
a(n) = Sum_{k=0..floor(n/5)} (n-4*k)!/k!.
|
|
2
|
|
|
1, 1, 2, 6, 24, 121, 722, 5046, 40344, 363000, 3629521, 39921843, 479041932, 6227383740, 87181920360, 1307714287321, 20923268909764, 355693655298260, 6402460885833720, 121646408103159240, 2432922931206035521, 51091297862251106885, 1124007130194903158430
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
0,3
|
|
LINKS
|
|
|
FORMULA
|
a(n) = (n-1) * a(n-1) + (n-2) * a(n-2) + (n-3) * a(n-3) + (n-4) * a(n-4) + (n-8) * a(n-5) - 4 * a(n-6) - 4 * a(n-7) - 4 * a(n-8) - 4 * a(n-9) + 5 for n > 8.
|
|
PROG
|
(PARI) a(n) = sum(k=0, n\5, (n-4*k)!/k!);
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|