The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A065726

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A065726

Primes p whose base-8 expansion is also the decimal expansion of a prime.
(history; published version)

#18 by Michael De Vlieger at Sat Mar 05 11:08:59 EST 2022

STATUS

reviewed

approved

#17 by Joerg Arndt at Sat Mar 05 04:01:09 EST 2022

STATUS

proposed

reviewed

#16 by Michel Marcus at Sat Mar 05 03:10:34 EST 2022

STATUS

editing

proposed

#15 by Michel Marcus at Sat Mar 05 03:10:27 EST 2022

PROG

(PARI) is(p, b=10, c=8)=isprime(vector(#d=digits(p, c), i, b^(#d-i))*d~)&&isprime(p) \\ This code can be used for other bases b, c when b>c. See A235265 for code also valid for b<c. \\ _M. F. Hasler_, Jan 12 2014

#14 by Michel Marcus at Sat Mar 05 03:09:38 EST 2022

COMMENTS

In general rebase notation (Marc LeBrun): p(n) p8 = (8) [p] (10).

STATUS

approved

editing

#13 by Bruno Berselli at Fri Jun 15 02:53:22 EDT 2018

STATUS

reviewed

approved

#12 by Michel Marcus at Fri Jun 15 01:41:53 EDT 2018

STATUS

proposed

reviewed

#11 by Jon E. Schoenfield at Thu Jun 14 21:47:14 EDT 2018

STATUS

editing

proposed

#10 by Jon E. Schoenfield at Thu Jun 14 21:47:11 EDT 2018

NAME

Primes p whose base -8 expansion is also the decimal expansion of a prime.

LINKS

Harry J. Smith, <a href="/A065726/b065726.txt">Table of n, a(n) for n = 1,...,1000</a>

EXAMPLE

E.g. , 787{_10} = 1423{_8} is prime but also , and so is 1423{_10}.

PROG

(PARI) baseE(x, b)= { local(d, e=0, f=1); while (x>0, d=x-b*(x\b); x\=b; e+=d*f; f*=10); return(e) } { n=0; for (m=1, 10^9, p=prime(m); b=baseE(p, 8); if (isprime(b), write("b065726.txt", n++, " ", p); if (n==1000, return)) ) } [From _\\ _Harry J. Smith_, Oct 28 2009]

AUTHOR

Patrick De Geest, Nov 15 2001.

STATUS

approved

editing

#9 by N. J. A. Sloane at Mon Jan 13 01:14:16 EST 2014

STATUS

proposed

approved