A336340 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

A336340

a(n) = (1/2)A336338(n).

4

1, 3, 5, 7, 8, 9, 10, 11, 12, 14, 16, 17, 18, 21, 24, 25, 26, 27, 28, 30, 31, 32, 36, 37, 38, 39, 40, 41, 48, 49, 52, 57, 60, 61, 62, 64, 65, 66, 69, 74, 76, 82, 83, 84, 85, 86, 87, 89, 91, 92, 93, 94, 95, 96, 97, 98, 101, 102, 103, 106, 109, 110, 111, 112

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Table of n, a(n) for n=1..64.

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, A336341.

Sequence in context: A102890 A008520 A217129 * A100318 A167707 A131903

Adjacent sequences: A336337 A336338 A336339 * A336341 A336342 A336343

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Oct 03 2020

STATUS

approved