A099861 a(n) = (2*n-1)-st composite number: a bisection of A002808.

4, 8, 10, 14, 16, 20, 22, 25, 27, 30, 33, 35, 38, 40, 44, 46, 49, 51, 54, 56, 58, 62, 64, 66, 69, 72, 75, 77, 80, 82, 85, 87, 90, 92, 94, 96, 99, 102, 105, 108, 111, 114, 116, 118, 120, 122, 124, 126, 129, 132, 134, 136, 140, 142, 144, 146, 148, 152, 154, 156, 159, 161

Offset: 1

Author

N. J. A. Sloane, Nov 19 2004

Keywords

• nonn
• easy

Examples

			a(1) = 4 is the first composite number.
		

Links

• A.H.M. Smeets, Table of n, a(n) for n = 1..20000

Crossrefs

Cf. A002808, A099862, A175228.

Programs

Maple

b:=proc(n) if isprime(n)=true then else n fi end: B:=[seq(b(n),n=2..250)]: seq(B[2*m-1],m=1..75); # Emeric Deutsch, Dec 09 2004

Mathematica

Partition[Select[Range[200], CompositeQ], 2][[All, 1]] (* Jean-François Alcover, Mar 22 2023 *)

Python

from sympy import composite
def A099861(n): return composite((n<<1)-1) # Chai Wah Wu, Nov 14 2024

Formula

a(n) = A175228(n+1). - A.H.M. Smeets, Aug 19 2019

Extensions

More terms from Emeric Deutsch, Dec 09 2004