A336339 Numbers composite(n) such that gcd(n,composite(n)) is even.

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

Links

Table of n, a(n) for n=1..56.

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

Cf. A002808, A336338, A336340, A336341.

Sequence in context: A037981 A044846 A037917 * A282146 A204879 A326696

Adjacent sequences: A336336 A336337 A336338 * A336340 A336341 A336342

Keyword

nonn,easy

Author

Clark Kimberling, Oct 03 2020

Status

approved