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

1,1

Links

Table of n, a(n) for n=1..54.

Formula

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

Example

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.

Mathematica

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

Crossrefs

Cf. A084126, A084127, A001358, A106554.

Sequence in context: A256619 A055109 A106552 * A304949 A316617 A303815

Adjacent sequences: A106547 A106548 A106549 * A106551 A106552 A106553

Keyword

base,easy,nonn

Author

Eric Angelini, May 09 2005

Extensions

More terms from Reinhard Zumkeller, May 19 2005

Typo corrected by James C. McMahon, Feb 06 2024

Status

approved