[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,

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":
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.


More information about the SeqFan mailing list