A272475 Numbers n such that 2^n-1 and 3^n-1 are not coprime.
4, 6, 8, 10, 11, 12, 16, 18, 20, 22, 23, 24, 28, 30, 32, 33, 35, 36, 40, 42, 43, 44, 46, 48, 50, 52, 54, 55, 56, 58, 60, 64, 66, 68, 69, 70, 72, 75, 76, 77, 78, 80, 82, 83, 84, 86, 88, 90, 92, 95, 96, 99, 100, 102, 104, 105, 106, 108, 110, 112, 114, 115, 116, 117
Offset: 1
Keywords
Examples
gcd(2^4-1, 3^4-1) = gcd(15,80) = 5, so a(1) = 4.
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Crossrefs
Cf. A263647.
Programs
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Magma
[n: n in [1..200] | not Gcd(2^n-1, 3^n-1) eq 1];
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Mathematica
Select[Range[200], ! GCD[2^# - 1, 3^# - 1] == 1 &]
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PARI
isok(n) = gcd(2^n-1, 3^n-1) != 1; \\ Michel Marcus, May 01 2016
Comments