A235636 - OEIS

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A235636

Primes whose base-6 representation is also the base-7 representation of a prime.

2, 3, 5, 17, 47, 71, 97, 101, 131, 157, 173, 191, 211, 251, 257, 277, 307, 311, 353, 367, 401, 421, 461, 487, 491, 563, 577, 601, 631, 643, 647, 683, 701, 743, 751, 761, 853, 857, 907, 911, 937, 953, 983, 1021, 1033, 1087, 1103, 1193, 1201, 1259, 1277, 1289, 1327, 1451, 1471, 1571, 1583, 1597, 1601, 1747, 1831, 1907, 1933

(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

Harvey P. Dale, Table of n, a(n) for n = 1..1000

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

EXAMPLE

17 = 25_6 and 25_7 = 19 are both prime.

MATHEMATICA

Select[Prime[Range[300]], PrimeQ[FromDigits[IntegerDigits[#, 6], 7]]&] (* Harvey P. Dale, Sep 17 2017 *)

PROG

(PARI) is(p, b=7, c=6)=isprime(vector(#d=digits(p, c), i, b^(#d-i))*d~)&&isprime(p) \\ Note: This code is only valid for b > c.

CROSSREFS

Cf. A235637, A235265, A235266, A152079, A235461 - A235482, A065720 - A065727, A235394, A235395, A089971 ⊂ A020449, A089981, A090707 - A091924, A235615 - A235639. See the LINK for further cross-references.

Sequence in context: A256426 A019350 A235630 * A268130 A103074 A173236

Adjacent sequences: A235633 A235634 A235635 * A235637 A235638 A235639

KEYWORD

nonn,base

AUTHOR

M. F. Hasler, Jan 13 2014

STATUS

approved