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a(n) = least k such that the remainder when 23^k is divided by k is n.
17

%I #22 Aug 01 2015 05:58:18

%S 2,3,5,19,262,17,58,9,10,13,14,55,86,12153,514,111823,95,25,30,12147,

%T 68,235,29,280517,56,27,502,16805,51,49,166,35,62,1837,38,977969,82,

%U 39,1370,289,122,9822698929535,65,133,697,161,303,19445,50,147,259,1247

%N a(n) = least k such that the remainder when 23^k is divided by k is n.

%H Max Alekseyev et al., <a href="/A128363/a128363_2.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[23, 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. A128361, A128362, A128364, A128365, A128366, A128367, A128368, A128369, A129370, A128371, A128372.

%Y Cf. A036236, A078457, A119678, A119679, A127816, A119715, A119714, A127817, A127818, A127819, A127820, A127821, A128154, A128155, A128156, A128157, A128158, A128159, A128160.

%Y Cf. A128149, A128150, A128172.

%K hard,nonn

%O 1,1

%A _Alexander Adamchuk_, Feb 27 2007

%E a(42), a(64) from _Hagen von Eitzen_, Aug 04 2009

%E a(750), a(770), a(234), a(274), a(406), a(600), a(610), a(754) from _Daniel Morel_, May 31, Aug 24, Sep 20 2010

%E a(84) from _Max Alekseyev_, Apr 13 2012