A083351 Numbers n such that 5*7^n + 2 is prime.

0, 1, 4, 9, 12, 25, 132, 192, 459, 10377, 45130, 63589, 83265

Offset

1,3

Comments

Values corresponding to 9, 12, 25, 132, 192 and 459 (389 digits) have been certified prime with Primo. There are no other terms <= 4000.

No other terms <= 10^5. - Tyler NeSmith

Links

Table of n, a(n) for n=1..13.

Example

7, 37, 12007, 201768037, 69206436007, 6705343098319824504037
are 5*7^0 + 2, 5*7^1 + 2, 5*7^4 + 2, 5*7^9 + 2, 5*7^12 + 2, 5*7^25 + 2,
respectively. 5*7^132 + 2 has 113 digits.

Prog

(PARI) for(n=0, 4000, if(isprime(5*7^n+2), print1(n, ", ")))

Crossrefs

Sequence in context: A344578 A283105 A179808 * A055381 A287498 A359301

Adjacent sequences: A083348 A083349 A083350 * A083352 A083353 A083354

Keyword

nonn

Author

Rick L. Shepherd, Apr 26 2003

Extensions

a(10)-a(13) from Tyler NeSmith, Jan 17 2021

Status

approved