OFFSET
1,2
COMMENTS
a(20) > 400000.
LINKS
MATHEMATICA
Select[Range[1, 10000], PrimeQ[n*18^n-1] &]
PROG
(PARI) for(n=1, 10000, if(isprime(n*18^n-1)), print1(n, ", ")))
(Magma) [n: n in [1..10000] |IsPrime(n*18^n-1)]
CROSSREFS
Numbers n such that n * b^n - 1 is prime: A008864 (b=1), A002234 (b=2), A006553 (b=3), A086661 (b=4), A059676 (b=5), A059675 (b=6), A242200 (b=7), A242201 (b=8), A242202 (b=9), A059671 (b=10), A299374 (b=11), A299375 (b=12), A299376 (b=13), A299377 (b=14), A299378 (b=15), A299379 (b=16), A299380 (b=17), this sequence (b=18), A299382 (b=19), A299383 (b=20).
KEYWORD
nonn,more,hard
AUTHOR
Tim Johannes Ohrtmann, Feb 08 2018
STATUS
approved