login
A367319
Base-2 Fermat pseudoprimes k such that (k-1)/ord(2, k) > (m-1)/ord(2, m) for all base-2 Fermat pseudoprimes m < k, where ord(2, k) is the multiplicative order of 2 modulo k.
2
341, 1105, 1387, 2047, 4369, 4681, 5461, 13981, 15709, 35333, 42799, 60787, 126217, 158369, 215265, 256999, 266305, 486737, 617093, 1082401, 1398101, 2113665, 2304167, 4025905, 4188889, 4670029, 6236473, 6242685, 8388607, 13757653, 16843009, 17895697, 22369621
OFFSET
1,1
MATHEMATICA
pspQ[n_] := CompositeQ[n] && PowerMod[2, n - 1, n] == 1; seq[kmax_] := Module[{s = {}, r, rm = 0}, Do[If[pspQ[k], r = (k - 1)/MultiplicativeOrder[2, k]; If[r > rm, rm = r; AppendTo[s, k]]], {k, 1, kmax}]; s]; seq[10^6]
PROG
(PARI) ispsp(n) = n > 1 && n % 2 && Mod(2, n)^(n-1) == 1 && !isprime(n);
lista(kmax) = {my(r, rm = 0); for(k = 1, kmax, if(ispsp(k), r = (k-1)/znorder(Mod(2, k)); if(r > rm, rm = r; print1(k, ", ")))); }
CROSSREFS
Subsequence of A001567.
Sequence in context: A271221 A066488 A291601 * A083876 A348258 A068216
KEYWORD
nonn
AUTHOR
Amiram Eldar, Nov 14 2023
STATUS
approved