A100802 a(n) = least k >= 0 such that (n+k)/2 is prime.

4, 3, 2, 1, 0, 1, 0, 3, 2, 1, 0, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 3, 2, 1, 0, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 3, 2, 1, 0, 7, 6, 5, 4, 3, 2, 1, 0, 11, 10, 9, 8, 7, 6, 5

Offset

0,1

Comments

If a(n) = k is nonzero then a(n+1) = k-1. a(2p) = 0 for p prime.

Links

Harvey P. Dale, Table of n, a(n) for n = 0..1000

Mathematica

a = {}; Do[k = 0; While[ ! PrimeQ[(n + k)/2], k++ ]; AppendTo[a, k]; , {n, 0, 120}]; a (* Ray Chandler, Jan 19 2005 *)
lk[n_]:=Module[{k=If[EvenQ[n], 0, 1]}, While[!PrimeQ[(n+k)/2], k=k+2]; k]; Array[lk, 120, 0] (* Harvey P. Dale, Nov 25 2016 *)

Crossrefs

Cf. A100803.

Sequence in context: A350493 A327351 A239475 * A022960 A023446 A258447

Adjacent sequences: A100799 A100800 A100801 * A100803 A100804 A100805

Keyword

nonn,easy

Author

Amarnath Murthy, Dec 18 2004

Extensions

Extended by Ray Chandler, Jan 19 2005

Status

approved