%I #29 Nov 15 2024 09:04:36
%S 4,8,10,14,16,20,22,25,27,30,33,35,38,40,44,46,49,51,54,56,58,62,64,
%T 66,69,72,75,77,80,82,85,87,90,92,94,96,99,102,105,108,111,114,116,
%U 118,120,122,124,126,129,132,134,136,140,142,144,146,148,152,154,156,159,161
%N a(n) = (2*n-1)-st composite number: a bisection of A002808.
%H A.H.M. Smeets, <a href="/A099861/b099861.txt">Table of n, a(n) for n = 1..20000</a>
%F a(n) = A175228(n+1). - _A.H.M. Smeets_, Aug 19 2019
%e a(1) = 4 is the first composite number.
%p 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
%t Partition[Select[Range[200], CompositeQ], 2][[All, 1]] (* _Jean-François Alcover_, Mar 22 2023 *)
%o (Python)
%o from sympy import composite
%o def A099861(n): return composite((n<<1)-1) # _Chai Wah Wu_, Nov 14 2024
%Y Cf. A002808, A099862, A175228.
%K nonn,easy
%O 1,1
%A _N. J. A. Sloane_, Nov 19 2004
%E More terms from _Emeric Deutsch_, Dec 09 2004