A381465 - OEIS

A381465

Semiprimes k such that 6*k + 1 is also a semiprime.

4, 9, 14, 15, 22, 34, 39, 49, 65, 69, 74, 82, 85, 86, 93, 94, 111, 133, 145, 158, 159, 183, 185, 194, 201, 203, 209, 214, 219, 226, 235, 259, 265, 267, 289, 299, 301, 303, 319, 321, 323, 326, 327, 334, 341, 346, 358, 361, 362, 365, 371, 377, 386, 393, 403, 407, 413, 415, 422, 427, 437, 469, 471

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

OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

a(3) = 14 is a term because 14 = 2 * 7 is a semiprime and 6 * 14 + 1 = 85 = 5 * 17 is also a semiprime.

MAPLE

select(t -> numtheory:-bigomega(t) = 2 and numtheory:-bigomega(6*t+1)=2, [$4..1000]);

MATHEMATICA

s = {}; Do[If[{2, 2} == PrimeOmega[{k, 6*k + 1}], AppendTo[s, k]], {k, 1000}] ; s

PROG

(PARI) isok(k) = (bigomega(k)==2) && (bigomega(6*k+1)==2); \\ Michel Marcus, Feb 26 2025

CROSSREFS

Cf. A001358, A007693, A111153, A111170.

Sequence in context: A091880 A141560 A071864 * A312987 A050986 A284956

Adjacent sequences: A381460 A381461 A381464 * A381466 A381467 A381468

KEYWORD

nonn,new

AUTHOR

Zak Seidov and Robert Israel, Feb 24 2025

STATUS

approved