A333788 Semiprimes whose both factors are Fermat primes.

9, 15, 25, 51, 85, 289, 771, 1285, 4369, 66049, 196611, 327685, 1114129, 16843009, 4295098369

Offset

1,1

Comments

Product of two, not necessarily distinct Fermat primes.

For the finiteness or non-finiteness of this sequence, see A019434.

Most terms are binary palindromes (in A006995), except among the fifteen known terms, these squares > 9 are not: 25, 289, 66049, 4295098369.

Because (as of Jan. 3, 2026) there are only five known Fermat primes, this sequence is probably full. - Harvey P. Dale, Jan 03 2026

Links

Table of n, a(n) for n=1..15.

Mathematica

Times@@@Tuples[{3, 5, 17, 257, 65537}, 2]//Union (* Harvey P. Dale, Jan 03 2026 *)

Crossrefs

Cf. A006995, A019434.

Subsequence of A334102.

Sequence in context: A109888 A193227 A014003 * A082549 A013569 A129401

Adjacent sequences: A333785 A333786 A333787 * A333789 A333790 A333791

Keyword

nonn

Author

Antti Karttunen, Apr 15 2020

Status

approved