A096840 a(n) = x is the least number such that around x^2 (the center) the number of primes is equal to n. The radius of neighborhood is ceiling(log(x^2)).

1, 6, 3, 2, 14, 36, 117, 1652, 9582, 41361, 908637, 36284185

Offset

0,2

Links

Table of n, a(n) for n=0..11.

Example

n=9: a(9) = 41361, center = 1710732321, radius = 22; the nine primes in the zone are {1710732299, 1710732307, 1710732311, 1710732313, 1710732319, 1710732323, 1710732329, 1710732337, 1710732343}.

Mathematica

f[n_] := (PrimePi[n^2 + Ceiling[ Log[n^2]]] - PrimePi[n^2 - Ceiling[ Log[n^2]] - 1]); t = Table[0, {15}]; Do[a = f[n]; If[a < 15 && t[[a + 1]] == 0, t[[a + 1]] = n], {n, 10^5}] (* Robert G. Wilson v, Jul 14 2004 *)

Crossrefs

Cf. A096509-A096523, A096830-A096839.

Sequence in context: A280680 A272083 A357614 * A096685 A307150 A195457

Adjacent sequences: A096837 A096838 A096839 * A096841 A096842 A096843

Keyword

more,nonn

Author

Labos Elemer, Jul 14 2004

Extensions

Offset corrected and a(11) from Donovan Johnson, Jul 11 2010

Status

approved