OFFSET
1,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1000
EXAMPLE
For n=10, 1<=i<j<=10, there are 28 distinct [i,j], i.e. 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 18, 20, 21, 24, 28, 30, 35, 36, 40, 42, 45, 56, 63, 70, 72, 90.
Hence a(10) = 28.
MAPLE
b:= proc(n) b(n):= {seq(ilcm(i, n), i=1..n-1)} end:
s:= proc(n) s(n):= `if`(n=0, {}, b(n) union s(n-1)) end:
a:= n-> nops(s(n)):
seq(a(n), n=1..80); # Alois P. Heinz, Apr 29 2014
MATHEMATICA
a[n_] := Table[LCM[i, j], {i, 1, n-1}, {j, i+1, n}] // Flatten // Union // Length;
Array[a, 100] (* Jean-François Alcover, Nov 07 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Han Hu, Apr 22 2014
EXTENSIONS
More terms from Alois P. Heinz, Apr 29 2014
STATUS
approved