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A099861
a(n) = (2*n-1)-st composite number: a bisection of A002808.
3
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
1,1
LINKS
FORMULA
a(n) = A175228(n+1). - A.H.M. Smeets, Aug 19 2019
EXAMPLE
a(1) = 4 is the first composite number.
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 *)
PROG
(Python)
from sympy import composite
def A099861(n): return composite((n<<1)-1) # Chai Wah Wu, Nov 14 2024
CROSSREFS
KEYWORD
nonn,easy,changed
AUTHOR
N. J. A. Sloane, Nov 19 2004
EXTENSIONS
More terms from Emeric Deutsch, Dec 09 2004
STATUS
approved