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A214799
Let S be a set of n positive numbers such that all n choose 2 pairwise GCD's are distinct, and let max(S) denote the largest element of S; a(n) is the minimal value of max(S) over all choices for S.
4
1, 2, 6, 18, 54, 120, 240, 480, 960, 1920
OFFSET
1,2
FORMULA
Conjecture: a(n) = 15 * 2^(n-3) for n >= 6 (Robert Israel)
EXAMPLE
n a(n) Example of S
---------------------------
1 1 {1}
2 2 {1,2}
3 6 {2,3,6}
4 18 {4,9,12,18}
5 54 {8,24,27,36,54}
6 120 {45,80,84,90,112,120}
7 240 {45,126,160,168,180,224,240}
8 480 {135,252,270,320,336,360,448,480}
9 960 {504, 640, 672, 720, 756, 810, 896, 945, 960}
10 1920 {1008, 1215, 1280, 1344, 1440, 1512, 1620, 1792, 1890, 1920}
CROSSREFS
Cf. A061799 (minimum of smallest element), A213918.
Sequence in context: A132790 A358417 A372899 * A072850 A254941 A182899
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Mar 07 2013
EXTENSIONS
a(4)-a(8) from Robert Israel, Mar 05 2013.
a(9)-a(10) from Giovanni Resta, Mar 06 2013
STATUS
approved