%I #10 Aug 01 2015 05:55:27

%S 19,3,17,6,15,7,13,9,11,18,7989,92,973,33,611,24,2661,382,559,21,

%T 96641237093,42,1887,94,155,27,60403,36,7971,74,1172954777,46,

%U 2470227509,122,45,116,1837,362,779,60,469,358,1275143,51,55,118,723,49

%N a(n) = least k such that the remainder when 20^k is divided by k is n.

%H Robert G. Wilson v, <a href="/A128160/a128160.txt">Table of n, a(n) for n = 1..10000 with -1 for large entries where a(n) has not yet been found</a>

%t t = Table[0, {10000} ]; k = 1; While[ k < 4000000000, a = PowerMod[20, k, k]; If[a < 10001 && t[[a]] == 0, t[[a]] = k; Print[{a, k}]]; k++ ]; t (* _Robert G. Wilson v_, Aug 04 2009 *)

%Y Cf. A036236, A078457, A119678, A119679, A127816, A119715, A119714, A127817, A127818, A127819, A127820, A127821, A128154, A128155, A128156, A128157, A128158, A128159.

%Y Cf. A128149, A128150.

%K hard,nonn

%O 1,1

%A _Alexander Adamchuk_, Feb 16 2007

%E More terms copied from a-file by _Hagen von Eitzen_, Oct 22 2009