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A336340
a(n) = (1/2)A336338(n).
4
1, 3, 5, 7, 8, 9, 10, 11, 12, 14, 16, 17, 18, 21, 24, 25, 26, 27, 28, 30, 31, 32, 36, 37, 38, 39, 40, 41, 48, 49, 52, 57, 60, 61, 62, 64, 65, 66, 69, 74, 76, 82, 83, 84, 85, 86, 87, 89, 91, 92, 93, 94, 95, 96, 97, 98, 101, 102, 103, 106, 109, 110, 111, 112
OFFSET
1,2
EXAMPLE
In the following table, c(n) = A002808(n) = composite(n).
n c(n) gcd(n, c(n))
1 4 1
2 6 2
3 8 1
4 9 1
5 10 5
6 12 6
2 and 6 are in A336338; 6 and 12 are in A336339; 1 and 3 are in A336340; 3 and 6 are in A336341.
MATHEMATICA
c = Select[Range[2, 200], ! PrimeQ[#] &]; (* A002808 *)
u = Select[Range[Length[c]], EvenQ[GCD[c[[#]], #]] &] (* A336338 *)
v = Table[c[[u[[n]]]], {n, 1, Length[u]}]; (* A336339 *)
u/2 (* A336340 *)
v/2 (* A336341 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Oct 03 2020
STATUS
approved