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

Author

Juri-Stepan Gerasimov, Aug 04 2010

Keywords

• nonn

Comments

Semiprimes m such that m-4 is also semiprime.

Examples

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

Links

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

Crossrefs

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

Programs

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 *)

Formula

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

Extensions

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