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
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
E.g., 11 = 23_4 and 23_7 = 17 both are prime.
MAPLE
filter:= proc(n) local L, m;
if not isprime(n) then return false fi;
L:= convert(n, base, 4);
isprime(add(L[i]*7^(i-1), i=1..nops(L)));
end proc:
select(filter, [2, seq(i, i=3..10000, 2)]); # Robert Israel, Jul 02 2018
PROG
(PARI) is(p, b=7, c=4)=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 13 2014
STATUS
approved