A276741 Integers n such that 10^n + 5^n + 2^n is a prime.

0, 1, 7, 31, 37, 71, 235, 515, 1199, 1815, 6587, 30429, 35589, 42147, 58571

Offset: 1

Author

René Gy, Sep 16 2016

Keywords

• hard
• more
• nonn

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

Crossrefs

Cf. A125706.

Programs

Mathematica

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

PARI

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

Extensions

a(11) from Felix Fröhlich, Sep 17 2016

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