A106550 a(n) = n-th semiprime + (concatenation of its two prime factors, smallest factor first).

26, 29, 42, 35, 41, 50, 58, 233, 80, 239, 344, 251, 92, 257, 352, 269, 126, 368, 566, 376, 287, 293, 578, 392, 311, 788, 323, 602, 329, 416, 804, 424, 341, 614, 359, 448, 638, 377, 836, 1232, 383, 464, 472, 852, 401, 488, 413, 1256, 674, 419, 686, 437, 512, 884

Offset: 1

Author

Eric Angelini, May 09 2005

Keywords

• base
• easy
• nonn

Examples

			First semiprime is 4; 4 is 2*2; 26=4+22.
Second semiprime is 6; 6 is 2*3; 29=6+23.
Third semiprime is 9; 9 is 3*3; 41=9+33.
Fourth semiprime is 10; 10 is 2*5; 35=10+25.
		

Crossrefs

Cf. A084126, A084127, A001358, A106554.

Programs

Mathematica

R=165;SP=Select[Range[R], PrimeOmega[#]==2&]; FromDigits@ Flatten[IntegerDigits@ Table[#1, {#2}] & @@@ FactorInteger@ #] & /@ SP +SP (* James C. McMahon, Feb 18 2024 *)

Formula

a(n) = A001358(n) + A106554(n). - Reinhard Zumkeller, May 19 2005

Extensions

More terms from Reinhard Zumkeller, May 19 2005

Typo corrected by James C. McMahon, Feb 06 2024