login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A106556 Smallest number formed by concatenating the two factors of a semiprime. 0
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 (list; graph; refs; listen; history; text; internal format)
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: A091404 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified November 25 16:38 EST 2014. Contains 249998 sequences.