A214054 Least m>0 such that n!!+m and n-m have a common divisor > 1.

1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1

Offset

1,2

Links

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

Example

For n=6: gcd(n!!+1,n-1) = 1 and gcd(n!!+2,n-2)=2, so that a(6)=2.

Mathematica

b[n_]:=n!!; c[n_]:=n;
t=Table[m=1; While[GCD[b[n]+m, c[n]-m]==1, m++]; m, {n, 1, 200}] (* A214054 *)
Flatten[Position[t, 1]] (* A214585 *)
Flatten[Position[t, 2]] (* A214586 *)

Crossrefs

Cf. A214585, A214586.

Sequence in context: A339890 A351408 A205788 * A330739 A076398 A086257

Adjacent sequences: A214051 A214052 A214053 * A214055 A214056 A214057

Keyword

nonn,easy

Author

Clark Kimberling, Jul 21 2012

Status

approved