A277370 Positive integers k that divide 7^k + 2.

1, 3, 15, 69, 2155, 34073, 876047637, 97090036327, 420397381695, 2125899832395, 3177544777277, 34434175473881, 40845965389135, 7267074621260963, 11720938824295035, 21419515204636141

Offset: 1

Author

Seiichi Manyama, Oct 11 2016

Keywords

• nonn
• more

Comments

All terms are odd.

Some larger terms: 5623143546839445899891, 46186634668308298262543001. - Max Alekseyev, Oct 18 2016

Examples

			7^3 + 2 = 345 = 3 * 115, so 3 is a term.
		

Crossrefs

Cf. A066438.

Cf. Solutions to 7^n == k (mod n): A277371 (k=-3), this sequence (k=-2), A015954 (k=-1), A067947 (k=1), A277401 (k=2), A277554 (k=3).

Programs

Mathematica

Select[Range[1, 9999, 2], Divisible[7^# + 2, #] &] (* Alonso del Arte, Oct 11 2016 *)

PARI

is(n) = Mod(7, n)^n==-2 \\ Felix Fröhlich, Oct 14 2016

Formula

A066438(a(n)) = a(n) - 2 for n > 1.

Extensions

a(8)-a(13) from Max Alekseyev, Oct 18 2016

a(14)-a(16) from Max Alekseyev, Dec 27 2024