A080152 Values of n corresponding to the primes given in A073640. The concatenation of the a(n) and a(n+1)th primes for any n is also prime.

1, 2, 4, 8, 11, 12, 18, 21, 31, 34, 46, 47, 50, 61, 78, 84, 85, 90, 99, 100, 101, 106, 110, 111, 114, 131, 133, 138, 141, 157, 159, 167, 169, 172, 175, 183, 197, 198, 211, 229, 231, 232, 233, 235, 260, 261, 269, 276, 285, 289, 295, 306, 322, 337, 339, 340, 347

Offset: 1

Author

Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 31 2003

Keywords

• nonn
• base

Examples

			E.g. For n=5: a(5)=11, a(6)=12 and the concatenation of 11th and 12th primes is 3137, which is also prime. The 5th and 6th terms in A073640 are 31 and 37.
		

Crossrefs

Cf. A073640.

Programs

Maple

nout := [1]: for n from 2 to 1000 do: p := ithprime(n): d := parse(cat(pout[nops(pout)],p)): if (isprime(d)) then nout := [op(nout),n]: fi: od:

Formula

A073640(n) = prime(a(n)), with a(n) the n-th term in this sequence.

Extensions

Edited by Charles R Greathouse IV, Apr 26 2010