A128360 Numbers k such that k divides 20^k - 1.

1, 19, 361, 6859, 130321, 2476099, 47045881, 148305659, 893871739, 2817807521, 4234136149, 10350100679, 16983563041, 53538342899, 80448586831, 196651912901, 322687697779, 815211156289, 1017228515081, 1432001198261, 1528523149789

Offset

1,2

Comments

19 divides a(n) for n > 1. All powers of 19 are terms. a(n) = 19^(n-1) for all to n < 8, while a(8) = A128356(8) = 148305659 = 410819*19^2.

Prime divisors of a(n) in the order of appearance are {19, 410819, 617311, 1508981, ...}. - Alexander Adamchuk, May 16 2010

Links

Table of n, a(n) for n=1..21.

Prog

(PARI) is(n)=Mod(20, n)^n==1 \\ Charles R Greathouse IV, Nov 04 2016

Crossrefs

Cf. A001029, A128358, A014960, A014956, A014951, A014949, A014946, A014945, A067945, A128357, A128356, A128400, A177920.

Sequence in context: A370148 A171293 A045609 * A001029 A057685 A243399

Adjacent sequences: A128357 A128358 A128359 * A128361 A128362 A128363

Keyword

nonn

Author

Alexander Adamchuk, Mar 02 2007

Extensions

a(9)-a(11) from Stefan Steinerberger, May 09 2007

a(12)-a(15) from Alexander Adamchuk, May 16 2010

Edited and a(16)-a(21) added by Max Alekseyev, Oct 02 2010

Status

approved