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Least m>0 such that 3^n-m and n-m are relatively prime.
5

%I #8 May 10 2016 10:01:36

%S 2,1,2,1,2,1,4,1,2,1,2,1,2,1,2,2,2,1,2,1,2,1,2,1,2,1,4,1,2,1,2,1,2,1,

%T 2,2,2,1,2,1,2,1,2,1,2,1,4,1,2,1,2,1,2,1,2,2,2,1,2,1,2,1,2,1,2,2,4,1,

%U 2,1,2,1,2,1,2,2,2,2,2,1,2,1,2,1,2,1,4

%N Least m>0 such that 3^n-m and n-m are relatively prime.

%H Clark Kimberling, <a href="/A214716/b214716.txt">Table of n, a(n) for n = 1..1000</a>

%e gcd(3^7-1,6) = 2, gcd(3^7-2,5) = 5, gcd(3^7-3,4) = 4, gcd(3^7-4,3) = 1, so a(7) = 4.

%t Table[m = 1; While[GCD[3^n - m, n - m] != 1, m++]; m, {n, 1, 140}]

%t lm[n_]:=Module[{m=1,n3=3^n},While[!CoprimeQ[n3-m,n-m],m++];m]; Array[ lm,90] (* _Harvey P. Dale_, May 10 2016 *)

%Y Cf. A214071, A214717.

%K nonn,easy

%O 1,1

%A _Clark Kimberling_, Jul 27 2012