OFFSET
0,5
COMMENTS
LINKS
Vladimir Letsko, Mathematical Marathon, Problem 183 (in Russian)
EXAMPLE
Let a < b < c < d. There are two possible ways to arrange the sums in nondecreasing order:
1) a+b <= a+c <= a+d <= b+c <= b+d <= c+d, (for instance, a = 1, b = 3, c = 4, d = 5);
2) a+b <= a+c <= b+c <= a+d <= b+d <= c+d, (for instance, a = 1, b = 2, c = 3, d = 5).
Hence a(4) = 2.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Vladimir Letsko, Nov 03 2013
EXTENSIONS
Term a(0)=1 prepended by Max Alekseyev, Feb 23 2014
STATUS
approved