OFFSET
1,2
COMMENTS
These are instances that show that the sequence is at most what is given: 1, 1+2, 1+2+4, 1+2+5+7, 1+2+6+12+14, 1+3+11+22+23+27, 1+2+6+22+44+46+54.
EXAMPLE
a(3)=4 because 1+2+3 = 2+2+2 but you can't write 1+2+4 as the sum of three numbers in {1,2,4} in another way.
a(4)=7 because, for instance, 2+4+5+6 = 2+5+5+5 but I'll let you check that you can't write 1+2+5+7 as the sum of four numbers in {1,2,5,7}, unless of course you take each one once.
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
Vincent Nesme (vnesme(AT)ens-lyon.fr), May 28 2005
STATUS
approved