A163754 Exactly two distinct primes occur as substrings of the digits of n.

13, 17, 25, 27, 29, 31, 32, 35, 43, 47, 52, 57, 59, 67, 71, 72, 75, 79, 83, 97, 103, 107, 112, 115, 119, 125, 129, 130, 133, 134, 136, 138, 143, 147, 151, 152, 159, 163, 170, 174, 176, 177, 178, 183, 191, 192, 195, 199, 203, 205, 207, 215, 219, 225, 245, 250

Offset

1,1

Comments

If n is a term, then so are 10*n, 10*n+4, 10*n+6 and 10*n+8. - Robert Israel, May 15 2020

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

By Robert Israel's comment, a(n) << n^k, where k = 1.4306... = log(10)/log(5) =

A154156. - Charles R Greathouse IV, May 15 2020

Example

a(3) = 25 because "2" and "5" are prime substrings of "25".

Maple

filter:= proc(n) local L, S, i, j, k;
  L:= convert(n, base, 10);
  nops(select(isprime, {seq(seq(add(L[i]*10^(i-j), i=j..k), j=1..k), k=1..nops(L))}))=2
end proc:
select(filter, [$1..300]); # Robert Israel, May 15 2020

Crossrefs

Cf. A154156.

Sequence in context: A145483 A349978 A125262 * A104278 A129070 A335036

Adjacent sequences: A163751 A163752 A163753 * A163755 A163756 A163757

Keyword

base,easy,nonn

Author

Gil Broussard, Aug 03 2009

Status

approved