# Semiprime's dividers concatenated

Eric Angelini keynews.tv at skynet.be
Mon May 9 17:04:33 CEST 2005

```Beautiful, just beautiful, thanks Robert!
Please, if you have time, submit to Neil,
I must leave my PC for a couple of hours...
Best,
É.
----- Original Message -----
From: "Robert G. Wilson v" <rgwv at rgwv.com>
To: "Eric Angelini" <keynews.tv at skynet.be>
Cc: <seqfan at ext.jussieu.fr>
Sent: Monday, May 09, 2005 4:56 PM
Subject: Re: Semiprime's dividers concatenated

> Dear Eric,
>
> Easy, just build it from the concatenation of the primes.
>
> Sort[ Flatten[ Table[ FromDigits[ Join[ IntegerDigits[ Prime[i]],
IntegerDigits[
> Prime[j]] ]], {i, 10}, {j, 10}] ]]
>
> 22, 23, 25, 27, 32, 33, 35, 37, 52, 53, 55, 57, 72, 73, 75, 77, 112, 113,
115,
> 117, 132, 133, 135, 137, 172, 173, 175, 177, 192, 193, 195, 197, 211, 213,
217,
> 219, 223, 229, 232, 233, 235, 237, 292, 293, 295, 297, 311, 313, 317, 319,
323,
> 329, 511, 513, 517, 519, 523, 529, 711, 713, 717, 719, 723, 729, 1111,
1113, 1117,
> 1119, 1123, 1129, 1311, 1313, 1317, 1319, 1323, 1329, 1711, 1713, 1717,
1719,
> 1723, 1729, 1911, 1913, 1917, 1919, 1923, 1929, 2311, 2313, 2317, 2319,
2323,
> 2329, 2911, 2913, 2917, 2919, 2923, 2929
>
> Sincerely, Bob.
>
>
> Eric Angelini wrote:
>
> > Hello SeqFan,
> > Here are the first semiprimes (A001358):
> > 4,6,9,10,14,15,21,22,25,26,33,34,35,38,39,46...
> >
> > I've just submitted to the OEIS quite a lot of
> > sequences dealing with the concatenation of the
> > dividers of the semiprimes, e.g.:
> > First semiprime is 4; 4 is 2x2 --> 22
> > Second semiprime is 6; 6 is 3x2 --> 32
> >                          or 2x3 --> 23
> > Third semiprime is 9; 9 is 3x3 --> 33
> > Fourth semiprime is 10; 10 is 2x5 --> 25
> >                            or 5x2 --> 52
> > etc.
> >
> > How would look an increasing sequence with
> > all such "concatenated dividers", starting
> > with the smallest one? I'm unable to build
> > it by hand, fearing as always to forget one
> > result behind...
> >
> > Best,
> > É.
> >
> >
> >
>
>

```