A160522 The n-th odd composite number minus the n-th even composite number.

5, 9, 13, 15, 15, 19, 19, 21, 25, 27, 27, 29, 29, 33, 33, 35, 39, 39, 41, 43, 43, 45, 45, 45, 47, 51, 55, 57, 57, 57, 57, 57, 57, 59, 61, 61, 65, 65, 65, 65, 69, 69, 71, 71, 73, 75, 75, 77, 77, 81, 81, 81, 81, 85, 89, 89, 89, 89, 89, 91, 91, 91, 91, 91, 93, 97, 99, 99, 103, 103

Offset

1,1

Links

K. Stern, Table of n, a(n) for n = 1..1000

Formula

a(n) = A071904(n) - A005843(n+1).

Mathematica

Last[t = GatherBy[Select[Range[4, 245], ! PrimeQ[#] &], OddQ]] - Take[First[t], Length[Last[t]]] (* Jayanta Basu, Aug 11 2013 *)

Prog

(MATLAB) composite function [a] = A160522(k) j = 1; n = 1; even = 4; while j < k n = n + 1; if isprime(n) == 1 else if mod(n, 2) == 0 else a(j, 1) = n - even; even = even + 2; j = j + 1; end end end
(PARI) m=70; v=vector(m); k=4; n=0; while(n<m, if(k%2>0&&!isprime(k), n++; v[n]=k-2*(n+1)); k++); v \\ Klaus Brockhaus, May 22 2009

Crossrefs

Cf. A002808, A005843, A071904, A047846.

Sequence in context: A325274 A303264 A165971 * A314651 A194371 A314652

Adjacent sequences: A160519 A160520 A160521 * A160523 A160524 A160525

Keyword

easy,nonn

Author

Kyle Stern, May 16 2009

Extensions

Extended and formula edited by Klaus Brockhaus, May 22 2009

Status

approved