A069688 Primes that yield another prime on placing a 3 on both sides (as leading and trailing digits).

5, 7, 31, 37, 41, 43, 53, 59, 61, 67, 73, 79, 83, 101, 103, 139, 151, 157, 179, 197, 223, 241, 257, 263, 269, 271, 283, 293, 307, 311, 349, 353, 389, 421, 431, 461, 467, 491, 557, 593, 599, 601, 607, 631, 643, 647, 683, 691, 701, 727, 757, 769, 811, 827, 839

Offset: 1

Author

Amarnath Murthy, Apr 06 2002

Keywords

• nonn
• base

Examples

			139 is a member as 31393 is also a prime.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A069687, A069689, A069690.

Programs

Mathematica

Select[ Range[1000], PrimeQ[ # ] && PrimeQ[ FromDigits[ Insert[ IntegerDigits[ # ], 3, {{1}, {-1}}]]] &]
Select[Prime[Range[200]],PrimeQ[FromDigits[Join[{3},IntegerDigits[#],{3}]]]&] (* Harvey P. Dale, Oct 24 2011 *)

Extensions

Edited and extended by Robert G. Wilson v, May 03 2002