A107645 - OEIS

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A107645

Numbers k such that the string 1311k is the decimal expansion of a prime number.

11, 13, 29, 43, 49, 71, 103, 109, 127, 131, 143, 173, 181, 217, 223, 229, 239, 241, 251, 259, 263, 287, 301, 307, 311, 341, 353, 367, 377, 383, 403, 407, 419, 433, 449, 473, 481, 493, 503, 509, 523, 547, 553, 559, 577, 599, 617, 619, 623, 643, 689, 691

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OFFSET

1,1

COMMENTS

11 and 13 are twin primes.

LINKS

Daniel Starodubtsev, Table of n, a(n) for n = 1..10000

EXAMPLE

k=71: 131171 is prime.

k=131: 1311131 is prime.

PROG

(Magma) [ n: n in [1..800] | IsPrime(Seqint(Intseq(n) cat [1, 1, 3, 1])) ];