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A235630 Primes whose base 7 representation is also the base 8 representation of a prime. 1
2, 3, 5, 17, 47, 71, 89, 101, 197, 229, 241, 269, 271, 337, 353, 383, 479, 521, 577, 607, 631, 647, 673, 677, 719, 743, 761, 827, 997, 1097, 1153, 1181, 1193, 1279, 1289, 1303, 1319, 1447, 1543, 1601, 1697, 1811, 1823, 1907, 1951, 1993, 2017, 2131, 2203, 2243, 2339, 2357, 2383, 2549 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=1..54.

M. F. Hasler, Primes whose base c expansion is also the base b expansion of a prime

EXAMPLE

E.g., 17 = 23[7] and 23[8] = 19 both are prime.

PROG

(PARI) is(p, b=8, c=7)=isprime(vector(#d=digits(p, c), i, b^(#d-i))*d~)&&isprime(p) \\ NB: This code is only valid for b>c.

CROSSREFS

Cf. A235622, A235265, A235266, A152079, A235461 - A235482, A065720 - A065727, A235394, A235395, A089971A020449, A089981, A090707 - A091924, A235615 - A235639. See the LINK for further cross-references.

Sequence in context: A243441 A256426 A019350 * A235636 A268130 A103074

Adjacent sequences:  A235627 A235628 A235629 * A235631 A235632 A235633

KEYWORD

nonn,base

AUTHOR

M. F. Hasler, Jan 13 2014

STATUS

approved

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Last modified February 15 16:25 EST 2019. Contains 320136 sequences. (Running on oeis4.)