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A176301
Numbers k such that the k-th semiprime + 2 is prime.
0
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
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
KEYWORD
nonn
AUTHOR
EXTENSIONS
Entries checked by R. J. Mathar, Apr 20 2010
STATUS
approved