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A271842 Positive numbers n such that n^2 - 1 divides 4^n - 1. 3
2, 4, 6, 16, 36, 52, 66, 256, 378, 456, 1296, 1470, 1548, 1800, 2002, 2556, 4356, 6480, 8008, 11952, 23580, 26320, 33930, 36636, 37170, 43290, 44100, 47520, 47880, 49680, 57240, 65536, 74448, 84420, 97812, 101920, 127050, 134946, 139860, 141156, 157080, 164880, 165600, 209220, 225456 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..1000
EXAMPLE
2 is in this sequence because (4^2 - 1)/(2^2 - 1) = 5.
MAPLE
A271842:=n->`if`((4^n-1) mod (n^2-1) = 0, n, NULL): seq(A271842(n), n=2..10^4); # Wesley Ivan Hurt, Apr 18 2016
MATHEMATICA
Select[Range[1, 100], IntegerQ[(4^# - 1)/(#^2 - 1)] &] (* G. C. Greubel, Apr 15 2016 *)
PROG
(Magma) [0] cat [n: n in [2..240000] | Denominator((4^n-1)/(n^2-1)) eq 1];
(PARI) is(n)=Mod(4, n^2-1)^n==1 \\ Charles R Greathouse IV, Apr 15 2016
CROSSREFS
Cf. positive numbers n such that n^2 - 1 divides (2^k)^n - 1:
A247219 (k=1), this sequence (k=2), A242062 (k=3).
Sequence in context: A167569 A032503 A050838 * A261864 A071243 A112086
KEYWORD
nonn
AUTHOR
STATUS
approved

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Last modified February 22 19:53 EST 2024. Contains 370260 sequences. (Running on oeis4.)