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
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Aug 04 2010
EXTENSIONS
Corrected (313 removed) by R. J. Mathar, Aug 07 2010
STATUS
approved