A176301 Numbers k such that the k-th semiprime + 2 is prime.

3, 6, 7, 13, 15, 18, 20, 23, 24, 26, 30, 34, 36, 43, 51, 54, 57, 68, 75, 78, 80, 86, 91, 98, 99, 106, 108, 116, 117, 118, 119, 125, 128, 132, 135, 138, 150, 151, 153, 154, 161, 171, 185, 186, 187, 192, 201, 204, 207, 212, 215, 217, 221, 223, 226, 228, 232, 233, 237

Offset

1,1

Links

Table of n, a(n) for n=1..59.

Example

3 is a term because A001358(3) + 2 = 11 (prime);
6 is a term because A001358(6) + 2 = 17 (prime).

Maple

isA001358 := proc(n) numtheory[bigomega](n) = 2 ; end proc:
A001358 := proc(n) option remember ; if n = 1 then return 4 ; else for a from procname(n-1)+1 do if isA001358(a) then return a; end if; end do; end if; end proc:
for n from 1 to 300 do if isprime( A001358(n)+2 ) then printf("%d, ", n) ; end if; end do: # R. J. Mathar, Apr 20 2010

Mathematica

Position[Select[Range[1000], PrimeOmega[#]==2&], _?(PrimeQ[#+2]&)]//Flatten (* Harvey P. Dale, Dec 01 2019 *)

Crossrefs

Cf. A001358 (semiprimes).

Cf. A176065.

Sequence in context: A350943 A282354 A088146 * A191290 A137595 A033053

Adjacent sequences: A176298 A176299 A176300 * A176302 A176303 A176304

Keyword

nonn

Author

Juri-Stepan Gerasimov, Apr 14 2010

Extensions

Entries checked by R. J. Mathar, Apr 20 2010

Status

approved