A113638 In the sequence of nonnegative integers subtract 1 from each prime number.

0, 1, 1, 2, 4, 4, 6, 6, 8, 9, 10, 10, 12, 12, 14, 15, 16, 16, 18, 18, 20, 21, 22, 22, 24, 25, 26, 27, 28, 28, 30, 30, 32, 33, 34, 35, 36, 36, 38, 39, 40, 40, 42, 42, 44, 45, 46, 46, 48, 49, 50, 51, 52, 52, 54, 55, 56, 57, 58, 58, 60, 60, 62, 63, 64, 65, 66, 66, 68, 69, 70, 70, 72

Offset: 0

Author

Cino Hilliard, Jan 15 2006

Keywords

• easy
• nonn

Crossrefs

Cf. A014684.

Programs

Mathematica

Table[If[PrimeQ[n],n-1,n],{n,0,80}] (* Harvey P. Dale, Sep 10 2017 *)

Python

from sympy import isprime
def A113638(n): return n-int(isprime(n)) # Chai Wah Wu, Oct 14 2023

Formula

a(n) = A014684(n), n>0. - R. J. Mathar, Aug 13 2008

Extensions

Name corrected by Wolfdieter Lang, Apr 22 2015