A089785 a(n) is the least prime(k) such that the concatenation of prime(k) and prime(k-n) is prime.

5, 7, 11, 19, 17, 19, 23, 29, 31, 37, 67, 43, 83, 61, 59, 61, 67, 79, 73, 113, 97, 167, 107, 101, 103, 149, 109, 137, 167, 163, 137, 179, 149, 163, 257, 179, 277, 173, 251, 199, 191, 193, 197, 199, 211, 229, 227, 229, 233, 239, 281, 347, 283, 263, 269, 271, 283

Offset: 1

Author

Amarnath Murthy, Nov 24 2003

Keywords

• base
• nonn

Examples

			a(4) = 19 =prime(8) and prime(8) followed by prime(8-4) =197 is prime.
		

Links

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

Crossrefs

Cf. A089782, A089783.

Programs

Maple

f:= proc(n) local p,k,q,d;
 p:= ithprime(n);
 for k from n+1 do
   p:= nextprime(p);
   q:= ithprime(k-n);
   d:= ilog10(q)+1;
   if isprime(p*10^d+q) then return p fi
 od
end proc:
map(f, [$1..100]); # Robert Israel, Dec 13 2017

Extensions

More terms from David Wasserman, Oct 13 2005