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A336338
Numbers k such that gcd(k, composite(k)) is even.
4
2, 6, 10, 14, 16, 18, 20, 22, 24, 28, 32, 34, 36, 42, 48, 50, 52, 54, 56, 60, 62, 64, 72, 74, 76, 78, 80, 82, 96, 98, 104, 114, 120, 122, 124, 128, 130, 132, 138, 148, 152, 164, 166, 168, 170, 172, 174, 178, 182, 184, 186, 188, 190, 192, 194, 196, 202, 204
OFFSET
1,1
EXAMPLE
In the following table, c(k) = A002808(k) = composite(k).
k c(k) gcd(k, c(k))
1 4 1
2 6 2
3 8 1
4 9 1
5 10 5
6 12 6
2 and 6 are in this sequence; 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