A049613 a(n) = 2n - (largest prime < 2n-2).

3, 3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 5, 7, 3, 3, 5, 7, 3, 5, 3, 3, 5, 3, 5, 7, 3, 5, 7, 3, 3, 5, 7, 3, 5, 3, 3, 5, 7, 3, 5, 3, 5, 7, 3, 5, 7, 9, 3, 5, 3, 3, 5, 3, 3, 5, 3, 5, 7, 9, 11, 13, 15, 3, 5, 3, 5, 7, 3, 3, 5, 7, 9, 11, 3, 3, 5, 7, 3, 5, 7, 3, 5, 3, 5, 7, 3, 5, 7, 3, 3, 5

Offset: 3

Author

David M. Elder (elddm(AT)rhodes.edu)

Keywords

• nice
• nonn
• easy

Examples

			a(14)=28 - (largest prime < 26) = 28 - 23 = 5.
		

Links

• T. D. Noe, Table of n, a(n) for n=3..10000

Crossrefs

Cf. A049653, A049711, A049716, A049847.

Cf. A002373, A020481, A007917.

Programs

Haskell

a049613 n = 2 * n - a007917 (2 * n - 2)
-- Reinhard Zumkeller, Jan 02 2015

Mathematica

Table[2n-NextPrime[2n-2,-1],{n,3,100}] (* Harvey P. Dale, Aug 16 2011 *)

Formula

a(n) <= A002373(n). - R. J. Mathar, Mar 19 2008

a(n) = 2*n - A007917(2*n-2). - Reinhard Zumkeller, Jan 02 2015