A128400 Numbers k such that k^2 divides 20^k - 1.

1, 19, 1432001198261, 3661225986659, 275941052631578947368421, 43838606653900416716028459121, 26357241068661238901986943659181

Offset

1,2

Comments

19 divides a(n) for n > 1.

Subsequence of A128360.

Links

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

Prog

(PARI) for( n=1, 10^6, Mod(20, n^2)^n - 1 || print1(n", ")) \\ M. F. Hasler, Oct 20 2008

Crossrefs

Cf. A128360, A127103, A127104, A127105, A127106, A127107, A127102, A127101, A127100, A127092, A128405, A128393, A128394, A128395, A128396, A128397, A128398, A128399, A128400, A128401, A128402, A128403, A128404.

Sequence in context: A038028 A013890 A347353 * A211378 A133591 A137643

Adjacent sequences: A128397 A128398 A128399 * A128401 A128402 A128403

Keyword

nonn,hard,more

Author

Alexander Adamchuk, Mar 08 2007

Extensions

a(4) from Max Alekseyev, Oct 18 2008

a(5)-a(7) from Max Alekseyev, May 06 2010

Status

approved