A051697 Closest prime to n (break ties by taking the smaller prime).

2, 2, 2, 3, 3, 5, 5, 7, 7, 7, 11, 11, 11, 13, 13, 13, 17, 17, 17, 19, 19, 19, 23, 23, 23, 23, 23, 29, 29, 29, 29, 31, 31, 31, 31, 37, 37, 37, 37, 37, 41, 41, 41, 43, 43, 43, 47, 47, 47, 47, 47, 53, 53, 53, 53, 53, 53, 59, 59, 59, 59, 61, 61, 61, 61, 67, 67, 67, 67, 67, 71, 71

Offset

0,1

Links

Table of n, a(n) for n=0..71.

Eric Weisstein's World of Mathematics, Nearest Prime

Example

Closest primes to 0,1,2,3,4 are 2,2,2,3,3.

Mathematica

a[n_] := (np = NextPrime[n]; pp = Prime[PrimePi[np] - 1]; Which[np > 2n-pp, pp, np < 2n-pp, np, True, pp]); a[0] = a[1] = 2; Table[a[n], {n, 0, 71}] (* Jean-François Alcover, Jul 28 2011 *)

Prog

(PARI) a(n)=if(n<3, return(2)); my(p=precprime(n), q=nextprime(n)); if(q-n<n-p, q, p) \\ Charles R Greathouse IV, Apr 28 2015

Crossrefs

Related sequences: A023186-A023188, A046929-A046931, A051650, A051652, A051697-A051702, A051728-A051730.

Sequence in context: A224908 A029097 A210955 * A240869 A367395 A065308

Adjacent sequences: A051694 A051695 A051696 * A051698 A051699 A051700

Keyword

nonn,easy

Author

N. J. A. Sloane

Extensions

More terms from James A. Sellers

Status

approved