A175664 Greater of twin semiprimes.

10, 14, 25, 26, 38, 39, 55, 62, 69, 86, 91, 95, 115, 119, 122, 123, 133, 145, 146, 159, 187, 205, 206, 209, 213, 217, 218, 219, 221, 253, 278, 291, 295, 299, 302, 303, 305, 309, 323, 327, 339, 362, 365, 381, 386, 395, 398, 407, 411, 415, 417, 451, 458, 473

Offset

1,1

Comments

Semiprimes m such that m-4 is also semiprime.

Links

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

Formula

a(n) = 4 + A175648(n). - R. J. Mathar, Aug 07 2010

Example

a(1)=10 because 10 (semiprime) - 4 = 6 (semiprime);
a(2)=14 because 14 (semiprime) - 4 = 10 (semiprime).

Maple

A175664 := proc(n) option remember; if n = 1 then 10; else for a from procname(n-1)+1 do if numtheory[bigomega](a) = 2 and numtheory[bigomega](a-4) = 2 then return a; end if; end do: end if; end proc: seq(A175664(n), n=1..100) ; # R. J. Mathar, Aug 07 2010

Mathematica

SequencePosition[Table[If[PrimeOmega[n]==2, 1, 0], {n, 500}], {1, _, _, _, 1}][[All, 2]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Dec 16 2017 *)

Crossrefs

Cf. A006512 (greater of twin primes), A175612 (list of twin semiprimes), A175648 (lesser of twin semiprimes).

Sequence in context: A168671 A136197 A071620 * A053690 A177948 A176140

Adjacent sequences: A175661 A175662 A175663 * A175665 A175666 A175667

Keyword

nonn

Author

Juri-Stepan Gerasimov, Aug 04 2010

Extensions

Corrected (313 removed) by R. J. Mathar, Aug 07 2010

Status

approved