A069689 Primes that yield another prime on placing a 7 on both sides (as leading and trailing digits).

2, 5, 17, 23, 29, 41, 47, 53, 71, 131, 191, 227, 233, 257, 281, 293, 347, 359, 389, 401, 419, 431, 479, 503, 521, 557, 593, 599, 653, 659, 677, 683, 701, 761, 797, 827, 857, 887, 953, 977, 1091, 1097, 1109, 1151, 1181, 1187, 1193, 1223, 1283, 1307, 1373

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

233 is a member as 72337 is also a prime.

Mathematica

Select[ Range[2000], PrimeQ[ # ] && PrimeQ[ FromDigits[ Insert[ IntegerDigits[ # ], 7, {{1}, {-1}}]]] &]
Select[Prime[Range[250]], PrimeQ[FromDigits[Join[{7}, IntegerDigits[ #], {7}]]]&]  (* Harvey P. Dale, Nov 01 2011 *)

Crossrefs

Cf. A069687, A069688 & A069690.

Sequence in context: A041283 A042049 A341017 * A307479 A106021 A032605

Adjacent sequences: A069686 A069687 A069688 * A069690 A069691 A069692

Keyword

nonn,base

Author

Amarnath Murthy, Apr 06 2002

Extensions

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

Status

approved