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A050717 Inserting a digit '7' between adjacent digits of n makes a prime. 0
13, 19, 21, 27, 33, 39, 49, 51, 57, 63, 67, 73, 87, 91, 97, 107, 137, 141, 147, 153, 159, 191, 197, 203, 207, 219, 221, 227, 249, 263, 273, 279, 311, 323, 327, 339, 351, 353, 359, 381, 389, 429, 477, 479, 497, 503, 507, 513, 519, 521, 533, 551, 569, 573, 593 (list; graph; refs; listen; history; internal format)
OFFSET

0,1

EXAMPLE

E.g. 477 becomes 4(7)7(7)7 which is prime 47777.

CROSSREFS

Cf. A050674, A050711-A050719.

Sequence in context: A119149 A171098 A118845 * A188540 A088184 A054986

Adjacent sequences:  A050714 A050715 A050716 * A050718 A050719 A050720

KEYWORD

nonn,base

AUTHOR

Patrick De Geest (pdg(AT)worldofnumbers.com), Aug 15 1999.

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Last modified February 16 09:00 EST 2012. Contains 205904 sequences.