A228076 Numbers k such that (19^k - 4^k)/15 is prime.
2, 7, 11, 31, 47, 139, 263, 769, 20551, 21491, 112247
Offset: 1
Programs
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Mathematica
Select[Prime[Range[1, 100000]], PrimeQ[(19^# - 4^#)/15]&]
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PARI
is(n)=ispseudoprime((19^n-4^n)/15) \\ Charles R Greathouse IV, Jun 13 2017
Extensions
a(11) from Robert Price, Mar 06 2021
Comments