A050719 Inserting a digit '9' between adjacent digits of n makes a prime.

11, 13, 17, 19, 23, 37, 41, 49, 53, 59, 61, 77, 91, 97, 131, 157, 167, 169, 173, 181, 191, 193, 197, 211, 227, 239, 259, 307, 311, 319, 323, 337, 349, 371, 379, 413, 419, 427, 431, 433, 449, 457, 467, 481, 491, 493, 499, 503, 517, 533, 539, 547, 563, 569, 571

Offset: 1

Author

Patrick De Geest, Aug 15 1999

Keywords

• nonn
• base

Examples

			181 becomes 1(9)8(9)1 which is prime 19891.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1001

Crossrefs

Cf. A050674, A050711, A050712, A050713, A050714, A050716, A050717, A050718, A050719.

Programs

Mathematica

Select[Range[10,1000],PrimeQ[FromDigits[Riffle[IntegerDigits[#],9]]]&] (* Harvey P. Dale, Oct 29 2014 *)

Extensions

Offset changed to 1 by Georg Fischer, Oct 15 2019