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A281120
For n odd, a(n) is the least positive integer not already used. For n even, a(n) is the least positive integer not already used that is not coprime to a(n/2).
2
2, 4, 3, 6, 5, 9, 7, 8, 10, 15, 11, 12, 13, 14, 16, 18, 17, 20, 19, 21, 22, 33, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 34, 51, 35, 36, 37, 38, 39, 42, 40, 44, 41, 45, 43, 46, 47, 48, 49, 50, 52, 54, 53, 57, 55, 56, 58, 87, 59, 60, 61, 62, 63, 64, 65, 66, 67
OFFSET
1,1
COMMENTS
In other words, gcd(a(n), a(2n)) > 1 for any n>0 (see A281121 for value of gcd(a(n), a(2n))).
This sequence cannot contain the value 1.
This sequence contains all values > 1.
This sequence is related to A082746: here we have gcd(a(n), a(2n)) > 1 and there we have gcd(a(n), a(2n)) = 1.
LINKS
EXAMPLE
Here is an illustration of the first terms:
n a(n) a(2n) gcd(a(n),a(2n))
-- ---- ----- ---------------
1 2 4 2
2 4 6 2
3 3 9 3
4 6 8 2
5 5 15 5
6 9 12 3
7 7 14 7
8 8 18 2
9 10 20 10
10 15 21 3
11 11 33 11
12 12 24 12
13 13 26 13
14 14 28 14
15 16 30 2
16 18 32 2
17 17 51 17
18 20 36 4
19 19 38 19
20 21 42 21
21 22 44 22
22 33 45 3
23 23 46 23
24 24 48 24
25 25 50 25
CROSSREFS
Sequence in context: A354373 A354374 A354453 * A246682 A143691 A129767
KEYWORD
nonn
AUTHOR
Rémy Sigrist, Jan 15 2017
STATUS
approved