A160709 Centuries containing a prime number of primes.

5, 14, 15, 20, 26, 30, 33, 35, 37, 39, 40, 45, 52, 55, 56, 60, 62, 63, 66, 70, 73, 75, 81, 87, 88, 89, 91, 93, 94, 96, 97, 98, 101, 108, 112, 115, 120, 122, 125, 131, 135, 140, 143, 155, 157, 166, 167, 168, 171, 175, 182, 183, 184, 185, 188, 189, 191, 192, 193, 196

Offset: 1

Author

Jonathan Vos Post, May 25 2009

Keywords

• easy
• nonn

Examples

			a(1) = 5 because 5 is the first Century to have a prime number (17) of primes.
		

Links

• H. v. Eitzen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A038822.

Programs

Maple

A038822 := proc(n) numtheory[pi](n*100)-numtheory[pi]((n-1)*100) ; end: A160709 := proc(n) option remember ; local a; if n = 1 then 5 ; else for a from procname(n-1)+1 do if isprime( A038822(a) ) then RETURN(a) ; fi; od: fi; end: seq(A160709(n),n=1...90) ; # R. J. Mathar, May 27 2009

Mathematica

Select[Range[200],PrimeQ[PrimePi[100#]-PrimePi[100(#-1)]]&] (* Harvey P. Dale, Oct 03 2011 *)

Formula

{n: A038822(n) is in A000040}.

Extensions

Extended by Ray Chandler, May 25 2009

More terms from R. J. Mathar, May 27 2009