OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..145 (terms below 10^11; terms 1..51 from Robert G. Wilson v)
Eric Weisstein's World of Mathematics, Fermat Pseudoprime.
MATHEMATICA
lst = {}; Do[ If[ PowerMod[19, 2n - 1, 2n] == 1, AppendTo[lst, 2n]], {n, 2, 2*10^9}]; lst (* Robert G. Wilson v, Jun 01 2007 *)
PROG
(PARI) is(k) = k > 2 && !(k % 2) && Mod(19, k)^(k-1) == 1; \\ Amiram Eldar, Sep 29 2024
CROSSREFS
Cf. A020147 = Pseudoprimes to base 19. Cf. A006935 = Even pseudoprimes (or primes) to base 2: n divides 2^n - 2, n even. Cf. A130433 = Even pseudoprimes to base 3. Cf. A090082 = Even pseudoprimes to base 5. Cf. A090083, A090084, A090085. Cf. A130434, A130435, A130436, A130438, A130439, A130440, A130441, A130442, A130443.
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, May 26 2007
EXTENSIONS
More terms from Robert G. Wilson v, Jun 01 2007
STATUS
approved