

A300327


Poulet numbers (Fermat pseudoprimes to base 2) with a record number of divisors that are also Poulet numbers.


1



341, 13981, 126217, 294409, 2113665, 4670029, 127479097, 140996401, 509033161, 8600780461, 42625846021, 220411358713, 2382784226641
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OFFSET

1,1


COMMENTS

The number of divisors is 1, 2, 3, 4, 5, 6, 7, 8, 13, 15, 16, 20, 23, ...


LINKS

Table of n, a(n) for n=1..13.
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

Cf. A001567, A290497.
Sequence in context: A210454 A069309 A086806 * A289305 A309285 A317556
Adjacent sequences: A300324 A300325 A300326 * A300328 A300329 A300330


KEYWORD

nonn,more


AUTHOR

Amiram Eldar, Mar 03 2018


STATUS

approved



