A109404 Numbers n such that sum of n-th and (n+1)-st semiprimes is a prime.

3, 5, 7, 8, 10, 11, 13, 22, 25, 27, 29, 37, 46, 51, 52, 76, 83, 86, 92, 104, 111, 113, 115, 123, 132, 140, 149, 190, 213, 218, 222, 233, 242, 274, 280, 281, 286, 298, 303, 307, 309, 336, 340, 346, 351, 379, 381, 395, 402, 415, 424, 444, 449, 463, 477, 478, 490

Offset: 1

Author

Zak Seidov, Jun 27 2005

Keywords

• nonn

Examples

			3 is OK because sp(3)=9, sp(3)=10 and 9+10=19 (prime); sp(n)=n-th semiprime.
		

Crossrefs

Cf. A092191 = numbers n such that sum of n-th and (n+1)-st semiprimes is a semiprime.

Programs

Mathematica

With[{semis=Partition[Select[Range[2000],PrimeOmega[#]==2&],2,1]}, Flatten[ Position[ semis,?(PrimeQ[Total[#]]&),{1},Heads->False]]] (* _Harvey P. Dale, May 01 2014 *)

PARI

lista(nn) = {vec = vector(nn, i, i); sp = select(i->(bigomega(i)==2), vec); for (i = 1, #sp-1, if (isprime(sp[i]+sp[i+1]), print1(i, ", ")););} \\ Michel Marcus, Oct 06 2013