A135590 Numbers k such that k^2 + 1 is a Sarrus number (pseudoprime to base 2).

216, 948, 1560, 4872, 8208, 9828, 18200, 29640, 37024, 65536, 89550, 283800, 535920, 592956, 649800, 825930, 1042320, 1382400, 1536220, 3688230, 4215120, 4321800, 5103210, 19078930, 21415680, 24471720, 214067490, 435457620, 535019100

Offset: 1

Author

Jason Earls, Feb 25 2008

Keywords

• nonn

Comments

Note that A000215(5) corresponds to a(10), and A000215(6) corresponds to a(33), and in general when A000215(n) is composite, this sequence has corresponding entry. - Jeppe Stig Nielsen, Mar 26 2016

Links

• Amiram Eldar, Table of n, a(n) for n = 1..40 (terms 1..33 from Jeppe Stig Nielsen)

Crossrefs

Cf. A000215, A001567, A002522, A005574.

Programs

Mathematica

fQ[n_] := ( !PrimeQ[n^2 + 1] && PowerMod[2, n^2, n^2 + 1] == 1); lst = {}; Do[ If[ fQ@ n, AppendTo[lst, n]], {n, 2, 440000000, 2}]; lst (* Robert G. Wilson v, Apr 18 2008 *)

PARI

is(n) = {Mod(2, n)^(n-1)==1 && !ispseudoprime(n) && n > 1};
for(n=1, 1e10, if(is(n^2+1), print1(n, ", "))); \\ Altug Alkan, Mar 26 2016

Extensions

More terms from Robert G. Wilson v, Apr 18 2008