login
A258778
Least base b >= 2 such that prime(n) is an absolute prime in base b.
2
3, 2, 3, 2, 5, 3, 5, 5, 4, 4, 2, 7, 7, 6, 7, 4, 8, 8, 9, 6, 8, 9, 11, 7, 7, 9, 11, 11, 13, 10, 2, 10, 12, 11, 13, 17, 12, 11, 12, 9, 16, 9, 6, 13, 15, 10, 6, 11, 19, 12, 19, 13, 11, 16, 7, 17, 19, 19, 12, 7, 16, 19, 7, 10, 13, 19, 22, 7, 19, 19, 18, 18, 21, 10
OFFSET
1,1
COMMENTS
a(n) < prime(n) for n > 1. This is true since prime(n) in base prime(n)-1 is written as 11 which is an absolute prime.
Conjecture: a(n) < prime(n)-1 for n > 2.
LINKS
EXAMPLE
a(78) = 13. prime(78) = 397 in base 10 and 397_10 = 247_13. Rearranging the digits in base 13, we get 274_13 = 433_10, 427_13 = 709_10, 472_13 = 769_10, 724_13 = 1213_10, 742_13 = 1237_10, all of which are prime.
CROSSREFS
KEYWORD
nonn
AUTHOR
Chai Wah Wu, Jun 11 2015
STATUS
approved