A210506 Numbers k such that (11^k - 2^k)/9 is prime.

2, 5, 11, 13, 331, 599, 18839, 23747, 24371, 29339, 32141, 67421

Offset: 1

Author

Robert Price, Jan 25 2013

Keywords

• hard
• more
• nonn

Comments

All terms are prime.

a(13) > 10^5.

Crossrefs

Cf. A004063, A028491, A057468, A059801, A121877, A128024, A128025, A128026, A128027, A128028, A128029, A128030, A128031, A128032.

Programs

Mathematica

Select[ Prime[ Range[1, 100000] ], PrimeQ[ (11^# - 2^#)/9 ]& ]

PARI

is(n)=isprime((11^n-2^n)/9) \\ Charles R Greathouse IV, Feb 17 2017