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1,2
Table of n, a(n) for n=1..7.
Table[If[PrimeQ[4*17^n-1], Print[n]; n], {n, 1, 20000}]
(PARI) is(n)=ispseudoprime(4*17^n-1) \\ Charles R Greathouse IV, Jun 13 2017
Cf. A180431 (numbers n such that 4*17^n + 1 is prime).
Cf. A205521 (numbers n such that 4*11^n - 1 is prime).
Cf. A046865 (numbers n such that 4*5^n - 1 is prime).
Cf. A005540 (numbers n such that 4*3^n - 1 is prime).
Sequence in context: A145923 A092562 A103602 * A081585 A227221 A273316
Adjacent sequences: A205793 A205794 A205795 * A205797 A205798 A205799
nonn
José María Grau Ribas, Jan 31 2012
approved