A265629 Numbers k > 0 such that 10^(k+4) - 23 is prime.

7, 13, 19, 31, 157, 761, 3469, 6883, 27677, 34309

Offset

1,1

Comments

Numbers k such that '9977' appended to k times the digit 9 is prime.

Up to a(8) the terms themselves are primes.

Links

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

Formula

a(n) mod 2 = 1. - Altug Alkan, Dec 14 2015

Example

7 appears because 99999999977 ('9' concatenated 7 times and prepended to '9977') is prime.

Maple

A265629:=n->`if`(isprime((10^(n+4) - 23), n, NULL): seq(A265629(n), n=1..1000)

Mathematica

Select[ Range[10^3], PrimeQ[10^(# + 4) - 23] &]

Prog

(Magma) [n: n in [1..200] | IsPrime(10^(n+4) - 23)];
(PARI) is(n)=isprime(10^(n+4) - 23)

Crossrefs

Cf. A260903.

Sequence in context: A023255 A373584 A122482 * A283191 A048375 A198035

Adjacent sequences: A265626 A265627 A265628 * A265630 A265631 A265632

Keyword

nonn,base,more,hard

Author

Mikk Heidemaa, Dec 11 2015

Extensions

a(10) from Michael S. Branicky, Nov 17 2024

Status

approved