A102501 Primes of the concatenated form 7nn7.

715157, 718187, 719197, 734347, 736367, 739397, 748487, 752527, 757577, 760607, 767677, 775757, 779797, 781817, 785857, 796967, 797977, 7100510057, 7102010207, 7103010307, 7104710477, 7105410547, 7106210627, 7106510657, 7107410747

Offset: 1

Author

Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 13 2005

Keywords

• easy
• nonn
• base

Examples

			715157 is prime and of the form 7nn7 for n=15.
7100510057 is prime and of the form 7nn7 for n=1005.
		

Links

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

Crossrefs

Cf. A102897 for sequence of all numbers of form 7nn7. A102500 for the n values corresponding to the primes in this sequence.

Programs

Mathematica

Select[Table[FromDigits[Join[{7},IntegerDigits[n],IntegerDigits[n],{7}]],{n,1100}],PrimeQ] (* Harvey P. Dale, Jun 05 2024 *)