OFFSET
1,1
COMMENTS
This sequence is part of the two-dimensional array of sequences 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
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
E.g., 19 = 23_8 and 23_7 = 17 are both prime.
MATHEMATICA
pb87Q[n_]:=Module[{idn8=IntegerDigits[n, 8]}, Max[idn8]<7&&PrimeQ[ FromDigits[ idn8, 7]]]; Select[Prime[Range[500]], pb87Q] (* Harvey P. Dale, Dec 13 2016 *)
PROG
(PARI) is(p, b=7, c=8)=vecmax(d=digits(p, c))<b&&isprime(vector(#d, i, b^(#d-i))*d~)&&isprime(p)
(PARI) forprime(p=1, 3e3, is(p, 8, 7)&&print1(vector(#d=digits(p, 7), i, 8^(#d-i))*d~, ", ")) \\ To produce the terms, this is more efficient than to select them using straightforwardly is(.)=is(., 7, 8)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
M. F. Hasler, Jan 13 2014
STATUS
approved