A160522 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

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

(Python)

def A160522(n):

if n == 1: return 5

m, k = n, primepi(n) + n + (n>>1)

while m != k:

m, k = k, primepi(k) + n + (k>>1)

return m-(n+1<<1) # Chai Wah Wu, Aug 01 2024

CROSSREFS

Cf. A002808, A005843, A071904, A047846.

Sequence in context: A325274 A303264 A165971 * A314651 A194371 A314652

Adjacent sequences: A160519 A160520 A160521 * A160523 A160524 A160525