A391332 Odd semiprimes k = p*q such that k = A325820(p,q), with p, q primes, where A325820 is the carryless base-3 multiplication.

9, 15, 21, 33, 39, 51, 57, 69, 87, 93, 111, 123, 129, 141, 159, 177, 183, 201, 213, 219, 237, 249, 267, 291, 303, 309, 321, 327, 339, 377, 381, 393, 403, 411, 417, 447, 453, 471, 481, 489, 501, 519, 537, 543, 573, 579, 591, 597, 633, 669, 681, 687, 699, 717, 723, 753, 771, 789, 807, 813, 831, 843, 849, 879, 921

Offset

1,1

Links

Antti Karttunen, Table of n, a(n) for n = 1..10000

Index entries for sequences related to carryless arithmetic.

Example

See example in A391331.

Prog

(PARI)
A325820_sq(b, c) = fromdigits(Vec(Pol(digits(b, 3))*Pol(digits(c, 3)))%3, 3);
is_A391332(n) = if(!(n%2) || 2!=bigomega(n), 0, my(f=factor(n), a = f[1, 1], b = f[#f~, 1]); (A325820_sq(a, b)==n));

Crossrefs

Cf. A325820.

Disjoint union of A001748\{6} and A391331 (terms that are not multiples of 3).

Subsequence of A391333.

Cf. also A365473 (analogous sequence for the carryless base-2 multiplication).

Sequence in context: A391333 A050991 A033553 * A020192 A241809 A063174

Adjacent sequences: A391329 A391330 A391331 * A391333 A391334 A391335

Keyword

nonn,base

Author

Antti Karttunen, Dec 07 2025

Status

approved