A338412 Numbers k such that k * 20^k + 1 is prime.

3, 6207, 8076, 22356, 151456

Offset: 1

Author

Tim Johannes Ohrtmann, Oct 25 2020

Keywords

• nonn
• more
• hard

Comments

a(6) > 219976.

Links

• Steven Harvey, Generalized Cullen Search
• G. Loeh, Generalized Cullen primes
• Wikipedia, Cullen number

Crossrefs

Numbers k such that k * b^k + 1 is prime: A006093 (b=1), A005849 (b=2), A006552 (b=3), A007646 (b=4), A242176 (b=6), A242177 (b=7), A242178 (b=8), A265013 (b=9), A007647(b=10), A242196(b=12), A242197 (b=14), A242198 (b=15), A242199 (b=16), A007648 (b=18), this sequence (b=20).

Programs

Magma

[n: n in [1..10000] |IsPrime(n*20^n+1)]

Mathematica

Select[Range[1, 10000], PrimeQ[n*20^n+1] &]

PARI

for(n=1, 10000, if(isprime(n*20^n+1), print1(n, ", ")))