OFFSET
1,2
EXAMPLE
a(6)=3 since, for S1={1,2,4}, we have 1=1, 2=2, 3=1+2, 4=4, 5=1+4 and 6=2+4 and no set S1 with fewer than three elements has the required property.
CROSSREFS
KEYWORD
nonn
AUTHOR
John W. Layman, Apr 24 2003
STATUS
approved