A185239 Numbers k such that (11^k + 10^k)/21 is prime.

53, 421, 647, 1601, 35527

Offset: 1

Author

Robert Price, Apr 05 2013

Keywords

• nonn
• more

Comments

All terms are prime.

a(6) > 10^5.

Crossrefs

Cf. A057178, A128341, A181141, A187819, A217095, A213216.

Programs

Mathematica

Select[ Prime[ Range[1, 100000] ], PrimeQ[ (11^# + 10^#)/21 ]& ]

PARI

is(n)=ispseudoprime((11^n+10^n)/21) \\ Charles R Greathouse IV, May 22 2017