OFFSET
1,1
COMMENTS
This sequence is part of a two-dimensional array of sequences, given in the LINK, based on this same idea for any two different bases b, c > 1. Sequence A235265 and A235266 are the most elementary ones in this list. Sequences A089971, A089981 and A090707 through A090721, and sequences A065720 - A065727, follow the same idea with one base equal to 10.
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..10000
EXAMPLE
7 = 21_3 and 21_5 = 11 are both prime, so 7 is a term.
MATHEMATICA
Select[Prime@ Range@ 500, PrimeQ@ FromDigits[ IntegerDigits[#, 3], 5] &] (* Giovanni Resta, Sep 12 2019 *)
PROG
(PARI) is(p, b=5, c=3)=isprime(vector(#d=digits(p, c), i, b^(#d-i))*d~)&&isprime(p) \\ Note: This code is only valid for b > c.
CROSSREFS
KEYWORD
nonn,base
AUTHOR
M. F. Hasler, Jan 12 2014
STATUS
approved