[seqfan] Re: Insert "+" and always get a prime

[Antreas Hatzipolakis]

And how about if the sign is "-" and take the absolute value?

APH



,Eric Angelini:


> Hello SeqFans,
> Look at those integers:
>
> 110,112,116,118,130,136
>
> You will always get a prime if you insert a "+" sign inside them, no
> matter where:
>
> 110 --> 1+10=11 and 11+0=11
> 112 --> 1+12=13 and 11+2=13
> 116 --> 17
> 118 --> 19
> 130 --> 1+30=31 and 13+0=13
> 136 --> 1+36=37 and 13+6=19
>
> 101 is not an integer with this property as 1+01=2 is not allowed (no
> substring starting with "0").
>
> I guess S, the sequence of integers that share this property) will start
> like this:
>
> S = 11, 12, 14, 16, 20, 21, 23, 25, 29, 30, 32, 34, 38, 41, 43, 47, 49,
> 50, 52, 56, 58, 61, 65, 67, 70, 74, 76, 83, 85, 89, 92, 94, 98, 110, 112,
> 116, 118, 130, 136,...
> Best,
> É.
>
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