A128358 Numbers k such that k divides 18^k - 1.

1, 17, 289, 4913, 83521, 1419857, 5846759, 24054337, 24137569, 99394903, 408923729, 410338673, 1689713351, 6951703393, 6975757441, 28725126967, 118178957681, 118285781329, 118587876497, 486643291847, 488327158439

Offset: 1

Author

Alexander Adamchuk, Mar 01 2007

Keywords

• hard
• nonn

Comments

17 divides a(n) for n > 1.

a(n) = 17^(n-1) for n < 7.

a(7) = 20231*17^2.

Crossrefs

Cf. A001026 (powers of 17), A015969 (k divides 16^k + 1).

Programs

PARI

is(n)=Mod(18,n)^n==1 \\ Charles R Greathouse IV, Nov 04 2016

Extensions

a(8)-a(10) from Farideh Firoozbakht, Mar 05 2007

a(11)-a(19) from Ryan Propper, Dec 31 2007

a(20)-a(24) from Alexander Adamchuk, May 17 2010