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A065725 Primes p such that the decimal expansion of its base 7 conversion is also prime. 3
2, 3, 5, 17, 29, 31, 43, 59, 71, 127, 157, 197, 211, 227, 239, 241, 337, 353, 367, 379, 409, 463, 491, 563, 577, 619, 647, 743, 757, 773, 787, 857, 911, 953, 967, 1093, 1123, 1163, 1193, 1249, 1303, 1373, 1429, 1459, 1471, 1499, 1583, 1597, 1613, 1627, 1669 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

In general rebase notation (Marc LeBrun): p(n) = (7) [p] (10).

LINKS

Harry J. Smith, Table of n, a(n) for n=1,...,1000

EXAMPLE

E.g. 787{10} = 2203{7} is prime but also 2203{10}.

MATHEMATICA

Select[ Range[2500], PrimeQ[ # ] && PrimeQ[ FromDigits[ IntegerDigits[ #, 7]]] & ]

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, 7); if (isprime(b), write("b065725.txt", n++, " ", p); if (n==1000, return)) ) } [From Harry J. Smith, Oct 27 2009]

CROSSREFS

Cf. A065720 up to A065727, A065361.

Sequence in context: A127061 A215311 A215315 * A057468 A127062 A214735

Adjacent sequences:  A065722 A065723 A065724 * A065726 A065727 A065728

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, Nov 15 2001.

STATUS

approved

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Last modified July 22 03:22 EDT 2017. Contains 289648 sequences.