A118769 Primes of the form n! - n!! + 1.

17, 673, 39937, 87177646081, 6402373519933441, 304888344611712432172380979201, 126886932185884164103433389335161480802865515044406852999479261820223930701069680640000001

Offset

1,1

Comments

The next term -- a(8) -- has 675 digits. - Harvey P. Dale, Dec 17 2018

References

G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 159.

Links

Table of n, a(n) for n=1..7.

Example

For n=4, 4! - 4!! + 1 = 4*3*2*1 - 4*2 + 1 = 24 - 8 + 1 = 17, which is prime.

Maple

SFACT:= proc(n) local i, j, k; for k from 1 by 1 to n do i:=k; j:=k-2; while j >0 do i:=i*j; j:=j-2; od: if isprime(k!-i+1) then print(k!-i+1); fi; od: end: SFACT(300);

Mathematica

Select[Table[n!-n!!+1, {n, 70}], PrimeQ] (* Harvey P. Dale, Dec 17 2018 *)

Crossrefs

Sequence in context: A350981 A063941 A089018 * A009158 A012050 A012157

Adjacent sequences: A118766 A118767 A118768 * A118770 A118771 A118772

Keyword

nonn

Author

Paolo P. Lava and Giorgio Balzarotti, May 22 2006

Status

approved