
EXAMPLE

a(1) is the number of sums made from [0]. No sums can be made from this because 0 is not being added to anything. So a(1) = 0.
a(2) is the number of sums made from [0,0] + [0,0]. The only possible sum is 0, so a(2) = 1.
a(3) is the number of sums made from [0,0,1] + [0,0,1] + [0,0,1]. The possible sums are 0, 1, 2, and 3, so a(3) = 4.
a(4) is the number of sums made from [0,0,1,4] + [0,0,1,4] + [0,0,1,4] + [0,0,1,4]. There are 14 different possible sums so a(4) = 14.
