A106556 Smallest number formed by concatenating the two factors of a semiprime.

22, 23, 33, 25, 27, 35, 37, 112, 55, 132, 113, 172, 57, 192, 133, 223, 77, 173, 115, 193, 229, 231, 135, 233, 237, 117, 241, 175, 243, 293, 137, 313, 247, 195, 253, 337, 235, 259, 177, 1111, 261, 341, 343, 197, 267, 347, 271, 1113, 295, 273, 315, 279, 353

Offset

1,1

Links

Table of n, a(n) for n=1..53.

Example

First semiprime is 4; 4 is 2*2 -> 22.
Second semiprime is 6; 6 is 2*3 -> 23.
...
Eighth semiprime is 22; 22 is 11*2 -> 112 (and not 211).

Mathematica

f[n_]:=Module[{ids=IntegerDigits/@Transpose[FactorInteger[n]][[1]], a, b}, a =FromDigits[ Join[ First[ids], Last[ids]]]; b=FromDigits[ Join[ Last[ids], First[ids]]]; Min[a, b]]; f/@Select[Range[200], PrimeOmega[#] ==2&] (* Harvey P. Dale, Jun 20 2011 *)

Crossrefs

Sequence in context: A260994 A114963 A146755 * A106554 A118297 A022392

Adjacent sequences: A106553 A106554 A106555 * A106557 A106558 A106559

Keyword

base,easy,nonn

Author

Eric Angelini, May 09 2005

Extensions

More terms from Harvey P. Dale, Jun 20 2011

Status

approved