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

1,1

Comments

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

Links

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

Formula

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

Example

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.

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 *)

Crossrefs

Cf. A065897, A000040, A141468.

Sequence in context: A349795 A005896 A147953 * A069183 A119907 A241335

Adjacent sequences: A163465 A163466 A163467 * A163469 A163470 A163471

Keyword

nonn,easy,less

Author

Juri-Stepan Gerasimov, Jul 28 2009

Extensions

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

Edited by Jon E. Schoenfield, Mar 04 2019

Status

approved