A175710 Numbers k such that k-4, k and k+4 are all semiprimes.

10, 91, 115, 119, 205, 209, 213, 217, 291, 295, 299, 305, 323, 407, 411, 485, 489, 493, 497, 501, 515, 533, 685, 699, 703, 717, 749, 767, 785, 789, 803, 917, 955, 989, 1007, 1077, 1115, 1137, 1141, 1145, 1195, 1199, 1203, 1207, 1257, 1267, 1333, 1343, 1347

Offset

1,1

Comments

If k is a term, one of k-4, k and k+4 is 3 times a prime. - Robert Israel, Mar 25 2025

Links

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

Example

a(1)=10 because 10-4=6, 10 and 10+4=14 are all semiprimes.

Maple

SP:= select(t -> numtheory:-bigomega(t) = 2, {$1..10000}):
sort(convert(SP intersect (SP +~ 4) intersect (SP -~ 4), list)); # Robert Israel, Mar 25 2025

Crossrefs

Cf. A001358, A175612, A175648, A175664.

Sequence in context: A374228 A116348 A043088 * A226389 A119047 A143572

Adjacent sequences: A175707 A175708 A175709 * A175711 A175712 A175713

Keyword

nonn

Author

Juri-Stepan Gerasimov, Aug 12 2010

Extensions

Corrected (299, 411 etc inserted) by R. J. Mathar, Aug 13 2010

Name edited by Robert Israel, Mar 25 2025

Status

approved