OFFSET
0,2
COMMENTS
Useful as a growth reference for sequences summing on intervals between 2 factorials.
LINKS
Iain Fox, Table of n, a(n) for n = 0..252
FORMULA
a(n) = 1/2 * ((n + 1)!*((n + 1)! + 1) - n!*(n! + 1) ).
EXAMPLE
a(2) = 3 + 4 + 5 + 6 = 18.
a(3) = 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20 + 21 + 22 + 23 + 24 = 24*25/2 - 6*7/2 = 279.
MATHEMATICA
Table[1/2 ((n + 1)! ((n + 1)! + 1) - n! (n! + 1) ), {n, 0, 10}]
PROG
(PARI) a(n) = 1/2*((n+1)!*((n+1)! + 1)-n!*(n!+1)) \\ Iain Fox, Nov 28 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Olivier Gérard, Oct 24 2017
EXTENSIONS
More terms from Iain Fox, Nov 28 2017
STATUS
approved