The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A231477 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A231477

Primes whose base-3 representation is also the base-7 representation of a prime.
(history; published version)

#15 by Jon E. Schoenfield at Sun Jan 16 23:09:20 EST 2022

STATUS

editing

approved

#14 by Jon E. Schoenfield at Sun Jan 16 23:09:18 EST 2022

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.

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approved

editing

#13 by Bruno Berselli at Thu Sep 12 04:45:18 EDT 2019

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proposed

approved

#12 by Giovanni Resta at Thu Sep 12 02:06:39 EDT 2019

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editing

proposed

#11 by Giovanni Resta at Thu Sep 12 02:06:33 EDT 2019

LINKS

Giovanni Resta, <a href="/A231477/b231477.txt">Table of n, a(n) for n = 1..10000</a>

MATHEMATICA

Select[Prime@Range@500, PrimeQ@FromDigits[IntegerDigits[#, 3], 7] &] (* Giovanni Resta, Sep 12 2019 *)

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proposed

editing

#10 by Michel Marcus at Thu Sep 12 01:54:14 EDT 2019

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editing

proposed

#9 by Michel Marcus at Thu Sep 12 01:54:11 EDT 2019

EXAMPLE

23 = 212_3 and 212_7 = 107 are both prime, so 23 is a term.

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proposed

editing

#8 by Michel Marcus at Thu Sep 12 01:09:16 EDT 2019

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editing

proposed

#7 by Michel Marcus at Thu Sep 12 01:09:12 EDT 2019

EXAMPLE

E.g., 23 = 212_3 and 212_7 = 107 are both prime.

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proposed

editing

#6 by Jon E. Schoenfield at Wed Sep 11 22:54:51 EDT 2019

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editing

proposed