

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
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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

Chai Wah Wu, Table of n, a(n) for n = 1..10000
Wikipedia, Permutable prime


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

Cf. A003459, A258706, A258802.
Sequence in context: A165258 A238393 A092962 * A112924 A267148 A230406
Adjacent sequences: A258775 A258776 A258777 * A258779 A258780 A258781


KEYWORD

nonn


AUTHOR

Chai Wah Wu, Jun 11 2015


STATUS

approved



