A287766 Numbers k such that (10^k*113 + 19)/3 is prime.

1, 9, 13, 33, 81, 1113, 1609, 5697, 13577, 49949

Offset

1,2

Comments

For k > 2, numbers such that '37'||...'6'...||'73' ('6' concatenated k-2 times and prefixed by '37', and suffixed by '73') in decimal form is prime.

Links

Table of n, a(n) for n=1..10.

Example

13 is in the sequence because (10^13*113 + 19)/3 = 376666666666673 is prime.

Mathematica

ParallelTable[ If[ PrimeQ[ (10^n*113+19)/3], n, Nothing], {n, 2000}]

Prog

(PARI) isok(n) = isprime((10^n*113 + 19)/3); \\ Michel Marcus, Jul 21 2017

Crossrefs

Cf. A051919, A101724.

Sequence in context: A031196 A151725 A146864 * A146739 A146723 A146422

Adjacent sequences: A287763 A287764 A287765 * A287767 A287768 A287769

Keyword

nonn,hard,more

Author

Mikk Heidemaa, May 31 2017

Status

approved