# [seqfan] Re: My first base-10 related question here, I think

Jack Brennen jfb at brennen.net
Fri Jun 26 00:59:07 CEST 2009

```Leroy Quet wrote:
> I usually loathe those base 10 sequences. But this sequence just isn't as interesting in base 2.
>
> Maybe this has been discussed here before. Probably, but I missed it then.
>
> Take all the primes written in base 10, and concatenate the list.
>
> 23571113171923293137...
>
> Next, starting on the left at the 2, place commas between the digits so that each comma is at the first place (the least amount of distance to the right) right of the last comma so that the digits in between the commas form primes.
>
> So we have the list of primes created:
>
> 2, 3, 5, 7, 11, 13, 17, 19,... (same as the original primes so far),
> then  2, 3, 2, then what? (The next prime starts with a 931...)
>

2
3
5
7
11
13
17
19
2
3
2
93137414347535961677173798389971011031071091131
2
7
13
11
3
7
13
91491511
5
7
163
167
17
3
17
9181
19
11
9319
7
19
9211223227229233239241251257
2
6326927
127
7
2
81283
2
93307
3
11
3
13
3
17
3
3
13
3
7
3
47
3
493533593673733
7
938338939
7
401
409
41
9421
43
1433
43
9443449457461
463
467
47
948749
149
9503509521523
5
41
5
47
5
5
7
5
6356957
157
7
5
87593599601607613617619631641
643
647
653
659
661
67
3
67
7
683
691
7
17
97
19
7
2
7
7
3
3
7
3
97
43
7
5
17
5
7
7
61
7
6977
3
7
877
97
809
811
821
823
827
829
83
9853857859863877881883887907911919929937941947953967971
97
7
983
991
997

GP program to print out the list:

a=0;

tryd(d) =
{
a=a*10+d;
if(isprime(a),print(a);a=0);
}

try(p) =
{
if(p>=10,try(p\10));
tryd(p%10);
}

forprime(p=2,1000,try(p));

```