# [seqfan] Re: Two neighboring digits sum up to a prime

Maximilian Hasler maximilian.hasler at gmail.com
Fri Apr 27 20:20:41 CEST 2012

```For any set = increasing sequence Axxx of OEIS, one could compute

>>> New sequence S: a(n) = smallest integer not yet in S such that two
>>> neighboring digits of S sum up to an element of Axxx

Well, actually the only thing that matters are the terms <= 18 in Axxx.

I wonder whether it makes sense to create the "new S" for any subset
of {0...18} which yields a nontrivial result....
But why not, after all this will yield a finite and relatively small

Maximilian

On Fri, Apr 27, 2012 at 11:45 AM, Jonathan Post <jvospost3 at gmail.com> wrote:
> Great!  Would you like to submit this to OEIS as by the two of us, as
> co-authors, Hans?
>
> On Fri, Apr 27, 2012 at 8:09 AM, Hans Havermann <gladhobo at teksavvy.com> wrote:
>> Jonathan Post:
>>
>>
>>> New sequence S: a(n) = smallest integer not yet in S such that two
>>> neighboring digits of S sum up to a semiprime  (4, 6, 9, 10, 14, or 15).
>>
>>
>>> This
>>> is to A001358 semiprimes as Eric Angelini's “Smallest integer not yet
>>> in S such that two neighboring digits of S sum up to a prime” is to
>>> A000040 Primes.
>>>
>>> Starting with 0:
>>>
>>> 0, 4, 2, 7, 3,  then seems to get stuck?
>>
>>
>> {0, 4, 2, 7, 3, 1, 5, 9, 6, 8, 13, 15, 18, 19, 51, 31, 33, 36, 37, 22, 24,
>> 27, 28, 60, 40, 42, 45, 46, 81, 54, 55, 59, 63, 64, 68, 69, 131, 82, 72, 73,
>> 77, 78, 133, 136, 86, 87, 222, 224, 227, 228, 137, 240, 90, 91, 95, 96, 313,
>> 151, 315, 154, 242, 245, 155, 159, 181, 318, 182, 246, 319, 186, 331, 333,
>> 187, 272, 273, 190, 404, 277, 278, 191, 336, 337, 281, 360, 406, 363, 195,
>> 196, 364, 282, 286, 368, 287, 369, 513, 372, 409, 515, 422, 424, 518, ...}
>>
>>
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>>
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>
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>
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```