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a(n) = (2*k)-th composite number; a bisection of A002808.
6

%I #25 Nov 15 2024 22:38:25

%S 6,9,12,15,18,21,24,26,28,32,34,36,39,42,45,48,50,52,55,57,60,63,65,

%T 68,70,74,76,78,81,84,86,88,91,93,95,98,100,104,106,110,112,115,117,

%U 119,121,123,125,128,130,133,135,138,141,143,145,147,150,153,155,158,160

%N a(n) = (2*k)-th composite number; a bisection of A002808.

%e a(1) = 6 is the second composite number.

%p c:=proc(n) if isprime(n) then else n fi end: B:=[seq(c(n),n=2..250)]: seq(B[2*m],m=1..75); # _Emeric Deutsch_, Dec 09 2004

%t Partition[Select[Range[200], CompositeQ], 2][[All, 2]] (* _Jean-François Alcover_, Mar 22 2023 *)

%Y Cf. A002808, A099861.

%Y Complement of A377898.

%K nonn,easy

%O 1,1

%A _N. J. A. Sloane_, Nov 19 2004

%E More terms from _Emeric Deutsch_, Dec 09 2004