A166160 a(n) = (n-th odd prime + n-th odd nonprime)/2 - 1.

1, 6, 10, 15, 18, 21, 25, 28, 33, 37, 42, 45, 48, 51, 57, 61, 64, 70, 73, 76, 81, 84, 89, 94, 97, 100, 105, 109, 113, 121, 124, 128, 130, 136, 139, 144, 148, 153, 157, 161, 163, 171, 173, 177, 179, 187, 195, 198, 201, 204, 210, 212, 218, 222, 228, 234, 236, 240, 243

Offset: 1

Author

Juri-Stepan Gerasimov, Oct 09 2009

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A001477, A005097, A014076, A047845, A065091.

Programs

Maple

A065091 := proc(n) ithprime(n+1) ; end proc:
A014076 := proc(n) if n = 1 then 1; else for a from procname(n-1)+2 by 2 do if not isprime(a) then return a ; end if; end do: end if; end proc:
A166160 := proc(n) (A065091(n)+A014076(n))/2-1 ; end proc: seq(A166160(n),n=1..120) ; # R. J. Mathar, May 21 2010

Mathematica

A014076 := Select[Range@250, ! PrimeQ@# && OddQ@# &]; A166160 := Prime[Range[2, 150]]; Table[(A166160[[n]] + A014076[[n]])/2 - 1, {n, 1, 50}] (* G. C. Greubel, Sep 17 2017 *)
Module[{nn=250,op,onp},op=Prime[Range[2,nn]];onp=Select[Range[1,nn,2],!PrimeQ[#]&];Total[#]/2-1&/@Thread[{Take[op,Length[ onp]],onp}]] (* Harvey P. Dale, Mar 02 2025 *)

Formula

a(n) = A005097(n) + A047845(n), where A005097 U A047845 = A001477.

a(n) = (A065091(n) + A014076(n))/2 - 1.

Extensions

Entries checked by R. J. Mathar, May 21 2010