A120387 c(n) mod b(n) where c(n) = (n-1)! and b(n) = Sum_{i=1..n} i.

0, 1, 2, 6, 9, 15, 20, 0, 0, 45, 54, 66, 77, 0, 0, 120, 135, 153, 170, 0, 0, 231, 252, 0, 0, 0, 0, 378, 405, 435, 464, 0, 0, 0, 0, 630, 665, 0, 0, 780, 819, 861, 902, 0, 0, 1035, 1080, 0, 0, 0, 0, 1326, 1377, 0, 0, 0, 0, 1653, 1710, 1770, 1829, 0, 0, 0, 0, 2145, 2210, 0, 0, 2415

Offset

1,3

Links

Table of n, a(n) for n=1..70.

Formula

For n>1: if neither n nor n+1 is prime, then a(n)=0. Otherwise, a(n)=n(n-1)/2 - 1 for odd n and a(n)=n(n-1)/2 for even n. - Ivan Neretin, May 29 2015

Example

a(5) = (5-1)! mod (1+2+3+4+5) = 24 mod 15 = 9.

Maple

P:=proc(n) local i, k; for i from 1 by 1 to n do print((i-1)! mod sum('k', 'k'=0..i)); od; end: P(100);

Crossrefs

Cf. A000217, A116536.

Cf. A226718, A119690.

Sequence in context: A363373 A353083 A049634 * A325761 A176039 A260699

Adjacent sequences: A120384 A120385 A120386 * A120388 A120389 A120390

Keyword

easy,nonn

Author

Paolo P. Lava, Jun 30 2006

Status

approved