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

1,1

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

Links

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

Example

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

Mathematica

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

Crossrefs

Cf. A071222, A195508.

Sequence in context: A226304 A101022 A241153 * A051064 A280509 A153096

Adjacent sequences: A213849 A213850 A213851 * A213853 A213854 A213855

Keyword

nonn,easy

Author

Clark Kimberling, Jul 26 2012

Status

approved