A300327 Poulet numbers (Fermat pseudoprimes to base 2) with a record number of divisors that are also Poulet numbers.

341, 13981, 126217, 294409, 2113665, 4670029, 127479097, 140996401, 509033161, 8600780461, 42625846021, 220411358713, 2382784226641, 11361630988981, 56308742593741, 431283945022021, 434124350060401, 2056455209005561, 5598600634063801, 8178192276975721

Offset: 1

Author

Amiram Eldar, Mar 03 2018

Keywords

• nonn

Comments

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

Examples

			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.
		

Links

• Daniel Suteu, Table of n, a(n) for n = 1..25
• Jan Feitsma and William F. Galway, Tables of pseudoprimes and related data.
• R. G. E. Pinch, Pseudoprimes up to 10^13.

Crossrefs

Cf. A001567, A290497.

Programs

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

Extensions

a(14)-a(20) from Daniel Suteu, Mar 06 2023