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A050719 Inserting a digit '9' between adjacent digits of n makes a prime. 22
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 0..1000

EXAMPLE

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

MATHEMATICA

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

CROSSREFS

Cf. A050674, A050711-A050718.

Sequence in context: A046117 A240900 A091923 * A217062 A244913 A098415

Adjacent sequences:  A050716 A050717 A050718 * A050720 A050721 A050722

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, Aug 15 1999.

STATUS

approved

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Last modified May 26 09:06 EDT 2017. Contains 287093 sequences.