A107643 Numbers n such that the string 75n is prime.

1, 7, 17, 23, 29, 37, 41, 47, 49, 59, 61, 73, 77, 83, 89, 91, 109, 133, 149, 161, 167, 169, 181, 193, 209, 211, 217, 223, 227, 239, 253, 269, 277, 289, 307, 323, 329, 337, 347, 353, 367, 377, 389, 391, 401, 403, 407, 431, 437, 479, 503, 511, 521, 527

Offset

1,2

Links

Table of n, a(n) for n=1..54.

Example

1 is a term as 751 is prime; 2 isn't, as 752 is composite; 37 is, as 7537 is prime.

Prog

(Sage) is_A107643 = lambda n: is_prime(Integer('75'+str(n))) # D. S. McNeil, Dec 10 2010
(Magma) [ n: n in [1..700] | IsPrime(Seqint(Intseq(n) cat [5, 7])) ]; // Vincenzo Librandi, Feb 02 2011

Crossrefs

Cf. A107642.

Sequence in context: A239210 A191087 A032454 * A289363 A319040 A216838

Adjacent sequences: A107640 A107641 A107642 * A107644 A107645 A107646

Keyword

nonn,base,less

Author

Parthasarathy Nambi, Jun 09 2005

Status

approved