A130440 - OEIS

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A130440

Even pseudoprimes to base 31.

6, 10, 30, 66, 946, 3310, 10470, 36370, 60126, 104106, 128766, 170710, 323670, 369370, 398266, 596926, 813430, 1145166, 1494690, 2384866, 5960746, 6376126, 8178346, 18327310, 31380922, 34102630, 37105762, 40796526, 41950966, 41983446

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OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..169 (terms below 10^11; terms 1..87 from Robert G. Wilson v)

Eric Weisstein's World of Mathematics, Fermat Pseudoprime.

Index entries for sequences related to pseudoprimes.

MATHEMATICA

Do[ f=PowerMod[ 31, 2n-1, 2n ]; If[ f==1, Print[ 2n ] ], {n, 2, 500000} ]

lst = {}; Do[ If[ PowerMod[31, 2n - 1, 2n] == 1, AppendTo[lst, 2n]], {n, 2, 2^31}]; lst (* Robert G. Wilson v, Jun 01 2007 *)

PROG

(PARI) is(k) = k > 2 && !(k % 2) && Mod(31, k)^(k-1) == 1; \\ Amiram Eldar, Sep 29 2024