A336338 Numbers k such that gcd(k, composite(k)) is even.

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

Links

Table of n, a(n) for n=1..58.

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

Cf. A002808, A336339, A336340, A336341.

Sequence in context: A302797 A355530 A130319 * A191256 A067368 A191259

Adjacent sequences: A336335 A336336 A336337 * A336339 A336340 A336341

Keyword

nonn,easy

Author

Clark Kimberling, Oct 03 2020

Status

approved