A163468 Indices k such that half of the k-th nonprime nonnegative integer is prime.

3, 4, 7, 9, 15, 18, 24, 27, 33, 43, 45, 54, 61, 64, 71, 80, 89, 93, 103, 109, 113, 122, 129, 139, 151, 157, 161, 168, 172, 179, 201, 208, 217, 220, 237, 241, 250, 261, 268, 279, 288, 291, 308, 311, 318, 321, 341, 361, 368, 371, 377, 388, 391, 408, 418, 428, 440

Offset: 1

Author

Juri-Stepan Gerasimov, Jul 28 2009

Keywords

• nonn
• easy
• less

Comments

Here k-th nonprime = A141468(k) (the k-th nonprime nonnegative integer).

Examples

			3 is a term because the 3rd nonprime nonnegative integer is 4, and 4/2 = 2 is prime.
4 is a term because the 4th nonprime nonnegative integer is 6, and 6/2 = 3 is prime.
7 is a term because the 7th nonprime nonnegative integer is 10, and 10/2 = 5 is prime.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A065897, A000040, A141468.

Programs

Maple

A141468 := proc(n) option remember ; if n = 1 then 0; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: for n from 1 to 600 do npr := A141468(n) ; if type(npr,'even') then if isprime(npr/2) then printf("%d,",n) ; fi; fi; od: # R. J. Mathar, Aug 01 2009

Mathematica

Flatten[Position[Select[Range[600],!PrimeQ[#]&],?(PrimeQ[#/2]&)]]+1 (* _Harvey P. Dale, May 05 2016 *)

Formula

a(n) = 2 + A065897(n). - R. J. Mathar, Aug 01 2009

Extensions

a(8) corrected by R. J. Mathar, Aug 01 2009

Edited by Jon E. Schoenfield, Mar 04 2019