A214716 Least m>0 such that 3^n-m and n-m are relatively prime.

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, 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, 2, 1, 2, 1, 2, 1, 2, 2, 2, 2, 2, 1, 2, 1, 2, 1, 2, 1, 4

Offset: 1

Author

Clark Kimberling, Jul 27 2012

Keywords

• nonn
• easy

Examples

			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.
		

Links

• Clark Kimberling, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A214071, A214717.

Programs

Mathematica

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