A213852 Least m>0 such that n+1+m and n-m are relatively prime.

2, 1, 1, 2, 1, 1, 3, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 3, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 3, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 5, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 3, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 3, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 3, 1, 1

Offset: 1

Author

Clark Kimberling, Jul 26 2012

Keywords

• nonn
• easy

Comments

a(n) > 1 for n == 1 mod 3, a(n) > 2 for n == 7 mod 15, a(n) > 3 for n == 52 mod 105, a(n) > 5 for n == 577 mod 1155, and so on, see A070826. - Ralf Stephan, Mar 16 2014

It appears that we get this sequence if we bisect A071222 and then divide by 2. - N. J. A. Sloane, May 17 2019

Examples

			gcd(9,6) = 3, gcd(10,5) = 5, gcd(11,4) = 1, so that a(7) = 3.
		

Links

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

Crossrefs

Cf. A071222, A195508.

Programs

Mathematica

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