A032662 a(n) is the least k such that k concatenated with k + n is prime.

1, 2, 1, 4, 3, 12, 1, 2, 1, 2, 3, 6, 1, 6, 3, 4, 5, 4, 5, 8, 7, 2, 21, 10, 17, 2, 1, 2, 3, 4, 1, 2, 7, 14, 3, 4, 1, 2, 1, 2, 11, 6, 5, 18, 3, 4, 3, 6, 1, 2, 1, 8, 5, 4, 7, 2, 1, 4, 5, 4, 11, 2, 1, 4, 3, 12, 1, 2, 9, 2, 3, 6, 1, 8, 9, 2, 3, 6, 1, 2, 1, 2, 5, 4, 929, 6, 3, 4, 5, 12, 1, 2, 1

Offset: 0

Author

Patrick De Geest, May 15 1998

Keywords

• nonn
• base
• look

Comments

First terms of sequences '1', A030457, A032617-A032624, continued with displacements d > 9.

Examples

			a(22) = 21: the concatenation of 21 and 21 + 22 = 43 is 2143 and this is a prime.
		

Links

• Robert Israel, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A032663.

Programs

Maple

tcat:= (a,b) -> a*10^(1+ilog10(b))+b:
f:= proc(n) local k;
  for k from 1 + (n mod 2) by 2 do
     if isprime(tcat(k,k+n)) then return k fi
  od;
end proc:
map(f, [$0..100]); # Robert Israel, Sep 05 2024

Extensions

Edited by Robert Israel, Sep 05 2024