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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 29 17:14 EDT 2020. Contains 337432 sequences. (Running on oeis4.)