A391330 Odd semiprimes that are not multiples of 3; Semiprimes congruent to 1 or 5 mod 6.

25, 35, 49, 55, 65, 77, 85, 91, 95, 115, 119, 121, 133, 143, 145, 155, 161, 169, 185, 187, 203, 205, 209, 215, 217, 221, 235, 247, 253, 259, 265, 287, 289, 295, 299, 301, 305, 319, 323, 329, 335, 341, 355, 361, 365, 371, 377, 391, 395, 403, 407, 413, 415, 427, 437, 445, 451, 469, 473, 481, 485, 493, 497, 505, 511

Offset

1,1

Comments

Question: Do the ratios A391328(n)/a(n) and A391335(n)/a(n) converge to about the same limit? [See the first and the third Plot2-links]

Links

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

Ratio A391328(n)/a(n), plotted with OEIS Plot2

Ratio A391329(n)/a(n), plotted with OEIS Plot2

Ratio A391335(n)/a(n), plotted with OEIS Plot2

Ratio A391337(n)/a(n), plotted with OEIS Plot2 (Does this converge to a limit?)

Mathematica

Select[Range[511], PrimeOmega[#]==2&&!Divisible[#, 2]&&!Divisible[#, 3]&] (* James C. McMahon, Dec 08 2025 *)

Prog

(PARI) is_A391330(n) = ((n%2) && (n%3) && 2==bigomega(n));

Crossrefs

Intersection of A001358 and A007310, intersection of A046315 and A176551.

Subsequence of A038509.

Subsequences: A391328, A391329, A391331, A391334, A391335, A391337.

Sequence in context: A038509 A067793 A287918 * A054550 A107472 A193165

Adjacent sequences: A391327 A391328 A391329 * A391331 A391332 A391333

Keyword

nonn

Author

Antti Karttunen, Dec 07 2025

Status

approved