A275542 - 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