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

Offset: 1

Author

Alexander Adamchuk, May 26 2007

Keywords

• nonn

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.

Crossrefs

Cf. A020159, A006935, A130433, A090082, A090083, A090084, A090085, A130434, A130435, A130436, A130437, A130438, A130439, A130441, A130442, A130443.

Programs

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 *)

PARI

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

Extensions

More terms from Robert G. Wilson v, Jun 01 2007