Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #35 Dec 28 2019 14:57:56
%S 2,3,5,7,2,3,5,7,2,2,2,2,2,3,2,2,5,2,2,7,2,2,3,3,3,2,3,3,3,3,5,3,3,7,
%T 3,3,2,3,5,7,5,5,5,2,5,3,5,5,5,5,5,7,5,5,2,3,5,7,7,7,7,2,7,3,7,7,5,7,
%U 7,7,7,7,2,3,5,7,2,3,5,7
%N The digits of the integers with the nonprimes removed.
%C Write the digits of the positive integers one by one: 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 0, 1, 1, 1, 2, 1, 3, 1, 4, 1, 5, 1, 6, 1, 7, 1, 8, 1, 9, 2, 0, 2, 1, etc. (this is A007376). Then from that sequence, remove the nonprimes, leaving a sequence that consists entirely of 2s, 3s, 5s and 7s.
%H Metin Sariyar, <a href="/A275542/b275542.txt">Table of n, a(n) for n = 1..32000</a> (terms 1..2401 from Robert Price)
%e From the single-digit numbers, we obviously get the first four terms of this sequence: 2, 3, 5, 7.
%e 10 is composite and neither of its digits is a single-digit prime, so it contributes nothing to this sequence.
%e 11 is prime but its digits consist of two 1s, so like 10 it also contributes nothing to the sequence.
%e 12 is composite, but its least significant digit is 2, which is a prime, and thus 12 contributes a 2 to the sequence.
%t Flatten[Table[Select[IntegerDigits[n], PrimeQ], {n, 100}]] (* _Alonso del Arte_, Aug 01 2016 *)
%Y Cf. A007376, A033307.
%K nonn,base
%O 1,1
%A _Dave Durgin_, Aug 01 2016