login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A268081 Least positive integer k such that 3^n-1 and k^n-1 are relatively prime. 1
2, 2, 2, 10, 2, 28, 2, 10, 2, 22, 10, 910, 2, 2, 2, 170, 2, 3458, 2, 110, 2, 46, 10, 910, 2, 2, 2, 290, 2, 9548, 2, 340, 10, 2, 22, 639730, 2, 2, 2, 4510, 2, 1204, 10, 230, 2, 94, 2, 216580, 2, 22, 2, 530, 2, 3458, 22, 580, 2, 118, 2, 18928910 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Note that (3^n-1)^n-1 is always relatively prime to 3^n-1.
According to the conjecture given in A086892, a(n) = 2 infinitely often.
When n>1, a(n) = 2 if and only if A260119(n) = 3.
LINKS
EXAMPLE
Since 3^5-1 = 242 and 2^5-1 = 31 are relatively prime, a(5) = 3.
MATHEMATICA
Table[k = 1; While[! CoprimeQ[3^n - 1, k^n - 1], k++]; k, {n, 59}] (* Michael De Vlieger, Jan 27 2016 *)
PROG
(Sage)
def min_k(n):
g, k=2, 0
while g!=1:
k=k+1
g=gcd(3^n-1, k^n-1)
return k
print([min_k(n) for n in [1..60]])
(PARI) a(n) = {k=1; while( gcd(3^n-1, k^n-1)!=1, k++); k; }
CROSSREFS
Sequence in context: A195706 A091185 A324956 * A319885 A368958 A125695
KEYWORD
nonn
AUTHOR
Tom Edgar, Jan 25 2016
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 16 08:27 EDT 2024. Contains 371698 sequences. (Running on oeis4.)