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A272366
Numbers n such that 5^n-4^(n+1) is prime.
0
7, 25, 29, 55, 75, 243, 345, 635, 899, 2025, 2105, 2295, 5057, 5155, 5209, 11115, 81743, 97615
OFFSET
1,1
COMMENTS
a(19) > 10^5.
EXAMPLE
7 is a member since 5^7 - 4^8 = 78125 - 65536 = 12589 which is a prime number.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[5^# - 4^(# + 1)] &]
PROG
(PARI) is(n)=ispseudoprime(5^n-4^(n+1)) \\ Charles R Greathouse IV, Jun 13 2017
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 27 2016
STATUS
approved