[seqfan] Primes with the next digit
Eric Angelini
Eric.Angelini at kntv.be
Thu Mar 22 16:15:42 CET 2012
Hello SeqFans,
Here is S, with a(n) being the smallest integer not yet in S and
such that the concatenation of a(n) and the first digit of a(n+1)
is a prime:
__
S = 1,3,7,9,70,10,11,30,71,90,72,73,31,12,74,33,13,75,14,91,15,16,
34,76,17,35,36,77,37,38,39,78,79,700,18,19,100,92,93,701,...
I must add: we want S to be infinite, else S would stop when the
next available a(n+1) is taken from A032352, "Numbers n such that
there is no prime between 10*n and 10*n+9":
https://oeis.org/A032352
__
This is why S(16) is "33" and not "32".
You will note, of course, that no a(n+1) starts with 2,4,5,6 or 8.
Best,
É.
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