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A075539
Perfect powers n such that (n-5)/2 is prime.
0
9, 27, 2187, 19683, 300763, 1092727, 2048383, 6128487, 15069223, 21717639, 24642171, 27818127, 36264691, 38958219, 54439939, 65450827, 84604519, 90224199, 112678587, 133432831, 139798359, 143055667, 163667323, 246491883, 313046839, 341532099, 347428927
OFFSET
1,1
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
KEYWORD
easy,nonn
AUTHOR
Zak Seidov, Oct 11 2002
EXTENSIONS
Extended by Robert G. Wilson v, Oct 14 2002
More terms from Sean A. Irvine, Feb 24 2025
STATUS
approved