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

Jonathan Post jvospost3 at gmail.com
Fri Apr 27 02:43:44 CEST 2012

```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, or 10).  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?

On Thu, Apr 26, 2012 at 5:23 PM, Neil Sloane <njasloane at gmail.com> wrote:
> Jim, Thanks for submitting these 3 sequences! (I'm mopping up some old
> emails)
> Neil
>
> On Mon, Apr 16, 2012 at 2:13 PM, Jim Nastos <nastos at gmail.com> wrote:
>
>> Hi Eric, everyone,
>>
>>  The set of numbers with the property that adjacent pairs of digits
>> sum to a prime is:
>>
>> 2 3 4 5 6 7 8 9 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 98 111 112 114 116 120 121
>> 123 125 129 141 143 147 149 161 165 167 200 202 203 205 207 211 212
>> 214 216 230 232 234 238 250 252 256 258 292 294 298 300 302 303 305
>> 307 320 321 323 325 329 341 343 347 349 383 385 389 411 412 414 416
>> 430 432 434 438 470 474 476 492 494 498 500 502 503 505 507 520 521
>> 523 525 529 561 565 567 583 585 589 611 612 614 616 650 652 656 658
>> 670 674 676 700 702 703 705 707 741 743 747 749 761 765 767 830 832
>> 834 838 850 852 856 858 892 894 898 920 921 923 925 929 941 943 947
>> 949 983 985 989
>> (not in OEIS, even if single-digit numbers are excluded)
>>
>>  Single digit numbers are included here because the set of possible
>> "adjacent-digit-sums" is an empty set. These are all the candidate
>> numbers for extended Eric Angelini's proposed sequence.
>>
>>  Starting with initial value of 1, Eric's sequence goes like this:
>> 1 2 3 4 7 6 5 8 9 20 21 11 12 14 16 50 23 25 29 41 43 47 49 83 85 61
>> 65 67 411 111 112 30 32 34 38 52 56 58 92 94 70 74 76 114 98 300 200
>> 202 116 120 203 89 205 207 412 121 123 211 125 212 129 214 141 143 216
>> 147 414 149 230 232 161 165 234 167 416 500 238 302 303 250 252 305
>> 256 502 307 430 258 320 292 321 294 323 298 325 611 432 329 434 341
>> 438 343
>> (not in OEIS: Eric's original message missed the 14 between 12 and 16.)
>>
>>  If one wants to start this off with 0 instead, then 0,1 is not prime,
>> so we go with 0,2 and run from there to create:
>> 0 2 1 4 3 8 5 6 7 41 11 12 9 20 21 14 16 50 23 25 29 43 47 49 83 85 61
>> 65 67 411 111 112 30 32 34 38 52 56 58 92 94 70 74 76 114 98 300 200
>> 202 116 120 203 89 205 207 412 121 123 211 125 212 129 214 141 143 216
>> 147 414 149 230 232 161 165 234 167 416 500 238 302 303 250 252 305
>> 256 502 307 430 258 320 292 321 294 323 298 325 611 432 329 434 341
>> 438 343
>> (not in OEIS.)
>>
>> I can submit these 3 sequences once my account is created (I haven't
>> submitted in almost 10 years.. I didn't need an account back then!)
>> J
>>
>> On Mon, Apr 16, 2012 at 9:42 AM, Eric Angelini <Eric.Angelini at kntv.be>
>> wrote:
>> > Hello SeqFans,
>> > this should be easy to extend:
>> >
>> > Smallest integer not yet in S such that two neighboring
>> > digits of S sum up to a prime:
>> >
>> > S = 1,2,3,4,7,6,5,8,9,20,21,11,12,16,50,23,25,29,41,43,47,49,...
>> > Best,
>> > É.
>> >
>> >
>> > _______________________________________________
>> >
>> > Seqfan Mailing list - http://list.seqfan.eu/
>>
>> _______________________________________________
>>
>> Seqfan Mailing list - http://list.seqfan.eu/
>>
>
>
>
> --
> Dear Friends, I will soon be retiring from AT&T. New coordinates:
>
> Neil J. A. Sloane, President, OEIS Foundation
> 11 South Adelaide Avenue, Highland Park, NJ 08904, USA