A100916 Sum of a semiprime and its semiprime index is a new semiprime.

10, 15, 25, 34, 46, 51, 55, 57, 69, 86, 91, 95, 106, 119, 121, 133, 141, 145, 155, 161, 166, 217, 218, 226, 247, 249, 253, 262, 274, 291, 298, 299, 302, 305, 341, 358, 365, 382, 407, 413, 445, 446, 481, 485, 501, 515, 533, 538, 543, 551, 559, 614, 623, 626

Offset: 1

Author

Ray Chandler, Nov 26 2004

Keywords

• easy
• nonn

Comments

This is the semiprime analog of A061067.

Examples

			a(1) = 10 because 10 = semiprime(4) and semiprime(4) + 4 = 14 is
semiprime.
a(2) = 15 because 15 = semiprime(6) and semiprime(6) + 6 = 21 is
semiprime.
		

Links

• Eric Weisstein, World of Mathematics, Semiprime.

Crossrefs

Cf. A001358, A061067, A100493, A100466, A100467, A100915.

Programs

Mathematica

Module[{sp=Select[Range[1000],PrimeOmega[#]==2&],len},len=Length[sp];Select[ Thread[{sp,Range[len]}],PrimeOmega[Total[#]]==2&]][[All,1]] (* Harvey P. Dale, Jan 13 2019 *)

Formula

a(n) = A100466(n) - A100915(n) = A001358(A100915(n)).