OFFSET
0,3
COMMENTS
EXAMPLE
a(1) is the number of repeating sums in the collection of all possible sums of [0] + [0]. There is only one possible sum here, 0+0. There are no repeats, so a(1) = 0.
a(2) is the number of repeating sums in the collection of all possible sums of [0,0] + [0,0]. The possible sums are 0+0, 0+0, and 0+0 (first+first, first+second, and second+second). There are two repeats, so a(2) = 2.
a(3) is the number of repeating sums in the collection of all possible sums of [0,0,2] + [0,0,2]. The possible sums are 0+0, 0+0, 0+2, 0+0, 0+2, and 2+2. There are 3 repeats, so a(3) = 3.
a(4) is the number of repeating sums in the collection of all possible sums of [0,0,2,3] + [0,0,2,3]. The possible sums are 0+0, 0+0, 0+2, 0+3, 0+0, 0+2, 0+3, 2+2, 2+3, and 3+3. There are 4 repeats, so a(4) = 4.
PROG
(PARI) v=[0]; n=1; while(n<75, w=[]; for(i=1, #v, for(j=i, #v, w=concat(w, v[i]+v[j]))); v=concat(v, #w-#vecsort(w, , 8)); n++); v
CROSSREFS
KEYWORD
nonn
AUTHOR
Derek Orr, Nov 22 2014
STATUS
approved