A238605 - OEIS

A238605

Semiprimes n such that (n+1)/4 also is a semiprime.

15, 35, 39, 55, 87, 155, 183, 203, 219, 247, 259, 295, 327, 339, 371, 471, 515, 535, 579, 583, 635, 707, 731, 803, 807, 835, 851, 871, 939, 995, 1011, 1047, 1059, 1067, 1111, 1147, 1191, 1195, 1203, 1207, 1211, 1219, 1255, 1315, 1339, 1355, 1363, 1383, 1507, 1527, 1563, 1591, 1643, 1651, 1687, 1707

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OFFSET

1,1

COMMENTS

A subsequence of Ruth-Aaron numbers A039752. The terms are by definition of the form n = 4k+3.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

MATHEMATICA

Select[Range[2000], PrimeOmega[#]==PrimeOmega[(#+1)/4]==2&] (* Harvey P. Dale, Oct 17 2021 *)

PROG

(PARI) forstep( n=3, 999, 4, bigomega(n)==2 & bigomega((n+1)/4)==2 && print1(n", "))

CROSSREFS