A336341 a(n) = (1/2)A336339(n).

3, 6, 9, 12, 13, 14, 16, 17, 18, 21, 24, 25, 26, 30, 34, 35, 37, 38, 39, 42, 43, 44, 49, 50, 52, 53, 55, 56, 64, 65, 69, 75, 79, 80, 81, 84, 85, 86, 90, 96, 99, 106, 107, 108, 109, 110, 111, 114, 117, 118, 119, 121, 122, 123, 124, 125, 129, 130, 131, 135

Offset

1,1

Links

Table of n, a(n) for n=1..60.

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, A336339, A336340.

Sequence in context: A297567 A285402 A153403 * A257220 A092452 A230215

Adjacent sequences: A336338 A336339 A336340 * A336342 A336343 A336344

Keyword

nonn,easy

Author

Clark Kimberling, Oct 03 2020

Status

approved