A090264 Numbers n such that the strings n7n and 7n7 are both prime.

131, 153, 191, 233, 261, 327, 341, 359, 389, 407, 429, 459, 489, 527, 533, 579, 593, 599, 671, 683, 701, 723, 731, 797, 813, 869, 873, 939, 981, 1083, 1097, 1109, 1143, 1187, 1241, 1283, 1317, 1391, 1437, 1451, 1539, 1553, 1871, 1889, 1893, 2049, 2111

Offset: 1

Author

Amarnath Murthy, Nov 28 2003

Keywords

• base
• nonn

Examples

			131 is a member as 1317131 and 71317 are both prime.
		

Links

• Daniel Starodubtsev, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A090262, A090263, A090265.

Extensions

More terms from mohammed bouayoun (bouyao(AT)wanadoo.fr), Feb 02 2004