Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 5000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
1,2
17 divides a(n) for n>1. a(n) = 17^(n-1) for n<7. a(7) = 20231*17^2.
Table of n, a(n) for n=1..21.
(PARI) is(n)=Mod(18, n)^n==1 \\ Charles R Greathouse IV, Nov 04 2016
Cf. A001026 = Powers of 17. Cf. A015969 = numbers n such that n | 16^n + 1.
Sequence in context: A045607 A045606 A171291 * A015969 A001026 A178765
Adjacent sequences: A128355 A128356 A128357 * A128359 A128360 A128361
hard,nonn
Alexander Adamchuk, Mar 01 2007
a(8)-a(10) from Farideh Firoozbakht, Mar 05 2007
More terms from Ryan Propper, Dec 31 2007
a(20)-a(24) from Alexander Adamchuk, May 17 2010
approved