A214056 Least m>0 such that 2^n+m and n-m have a common divisor > 1.

1, 2, 3, 2, 5, 1, 1, 2, 9, 2, 11, 2, 1, 2, 15, 2, 3, 2, 1, 2, 8, 2, 23, 2, 1, 1, 2, 2, 29, 2, 1, 2, 3, 2, 35, 2, 1, 2, 39, 2, 41, 2, 1, 2, 1, 1, 2, 2, 1, 2, 14, 1, 2, 2, 1, 2, 57, 2, 3, 2, 1, 2, 63, 2, 65, 1, 1, 2, 6, 2, 6, 2, 1, 2, 75, 2, 77, 2, 1, 2, 81, 2

Offset

1,2

Links

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

Example

gcd(2^4+1,4-1) = 1 and gcd(2^4+2,4-2) = 2, so a(4) = 2.

Mathematica

b[n_] := 2^n; c[n_] := n;
Table[m = 1; While[GCD[b[n] + m, c[n] - m] == 1, m++]; m, {n, 1, 100}]

Crossrefs

Cf. A214057.

Sequence in context: A120007 A092509 A214053 * A368900 A014973 A276835

Adjacent sequences: A214053 A214054 A214055 * A214057 A214058 A214059

Keyword

nonn,easy

Author

Clark Kimberling, Jul 22 2012

Status

approved