A075539 Perfect powers n such that (n-5)/2 is prime.

9, 27, 2187, 19683, 300763, 1092727, 2048383, 6128487

Offset

1,1

Links

Table of n, a(n) for n=1..8.

Example

9=3^2, 27=3^3, 2187=3^7, 19683=3^9, but 300763=67^3 - is there any rule?

Mathematica

pp = Join[{1}, Select[ Range[10^7], Apply[GCD, Last[ Transpose[ FactorInteger[ # ]]]] > 1 & ]]; Select[pp, PrimeQ[(# - 5)/2] & ]

Crossrefs

Sequence in context: A020254 A124396 A020281 * A225300 A053825 A328640

Adjacent sequences: A075536 A075537 A075538 * A075540 A075541 A075542

Keyword

easy,nonn

Author

Zak Seidov, Oct 11 2002

Extensions

Extended by Robert G. Wilson v, Oct 14 2002

Status

approved