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A276741 Integers n such that 10^n + 5^n + 2^n is a prime. 0
0, 1, 7, 31, 37, 71, 235, 515, 1199, 1815, 6587, 30429, 35589, 42147, 58571 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Corresponding primes of the form 10^n + 5^n + 2^n are {3, 17, 10078253, 10000000004656612873079540061773,  10000000000072759576141834396472156597, 100000000000000000000042351647362715016953416125036343281344004402684973, ...}

a(12) > 10000 if it exists. - Felix Fröhlich, Sep 17 2016

a(16) > 100000. - Robert Price, Dec 29 2016

LINKS

Table of n, a(n) for n=1..15.

MATHEMATICA

Do[f=10^n+5^n+2^n; If[PrimeQ[f], Print[{n, f}]], {n, 1, 2000}]

PROG

(PARI) is(n) = ispseudoprime(10^n+5^n+2^n) \\ Felix Fröhlich, Sep 17 2016

CROSSREFS

Cf. A125706.

Sequence in context: A241101 A238664 A272201 * A000696 A171733 A128028

Adjacent sequences:  A276738 A276739 A276740 * A276742 A276743 A276744

KEYWORD

hard,more,nonn

AUTHOR

René Gy, Sep 16 2016

EXTENSIONS

a(11) from Felix Fröhlich, Sep 17 2016

a(12)-a(15) from Robert Price, Dec 29 2016

STATUS

approved

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Last modified October 23 16:15 EDT 2018. Contains 316529 sequences. (Running on oeis4.)