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A300327
Poulet numbers (Fermat pseudoprimes to base 2) with a record number of divisors that are also Poulet numbers.
2
341, 13981, 126217, 294409, 2113665, 4670029, 127479097, 140996401, 509033161, 8600780461, 42625846021, 220411358713, 2382784226641, 11361630988981, 56308742593741, 431283945022021, 434124350060401, 2056455209005561, 5598600634063801, 8178192276975721
OFFSET
1,1
COMMENTS
The number of divisors is 1, 2, 3, 4, 5, 6, 7, 8, 13, 15, 16, 20, 23, ...
LINKS
Jan Feitsma and William F. Galway, Tables of pseudoprimes and related data.
R. G. E. Pinch, Pseudoprimes up to 10^13.
EXAMPLE
294409 is in the sequence since it is a Poulet number, and 4 of its divisors are also Poulet numbers (2701, 4033, 7957, 294409), more than for any smaller Poulet number.
PROG
(PARI) isP(n) = {Mod(2, n)^n==2 & !isprime(n) & n>1};
lista(nn) = {rec = 0; for (n=1, nn, if (isP(n), nb = sumdiv(n, d, isP(d)); if (nb > rec, print1(n, ", "); rec = nb); ); ); } \\ Michel Marcus, Mar 07 2018
CROSSREFS
Sequence in context: A069309 A353021 A086806 * A289305 A309285 A317556
KEYWORD
nonn
AUTHOR
Amiram Eldar, Mar 03 2018
EXTENSIONS
a(14)-a(20) from Daniel Suteu, Mar 06 2023
STATUS
approved