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A336339
Numbers composite(n) such that gcd(n,composite(n)) is even.
4
6, 12, 18, 24, 26, 28, 32, 34, 36, 42, 48, 50, 52, 60, 68, 70, 74, 76, 78, 84, 86, 88, 98, 100, 104, 106, 110, 112, 128, 130, 138, 150, 158, 160, 162, 168, 170, 172, 180, 192, 198, 212, 214, 216, 218, 220, 222, 228, 234, 236, 238, 242, 244, 246, 248, 250
OFFSET
1,1
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