A247211 a(0) = 0. a(n) is the number of repeating sums made from [a(0), ... a(n-1)] + [a(0), ... a(n-1)] + ... + [a(0), ... a(n-1)], where [a(0), ... a(n-1)] is repeated n times.

0, 0, 2, 6, 23, 80, 302, 1160, 4504, 17087, 66327

Offset

0,3

Comments

a(i)+a(j) and a(j)+a(i) are considered to be the same sum for all indices i and j.

Links

Table of n, a(n) for n=0..10.

Example

a(1) is the number of repeating 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 repeating sums made from [0,0] + [0,0]. The possible sums are 0+0, 0+0, and 0+0, so a(2) = 2.
a(3) is the number of repeating sums made from [0,0,2] + [0,0,2] + [0,0,2]. The possible sums are 0+0+0, 0+0+0, 0+0+2, 0+0+0, 0+0+2, 0+2+2, 0+0+0, 0+0+2, 0+2+2, and 2+2+2. There are 6 repeating sums so a(3) = 6.
a(4) is the number of repeating sums made from [0,0,2,6] + [0,0,2,6] + [0,0,2,6] + [0,0,2,6]. There are 23 repeating sums, so a(4) = 23.

Crossrefs

Sequence in context: A220213 A217200 A110068 * A150275 A335537 A150276

Adjacent sequences: A247208 A247209 A247210 * A247212 A247213 A247214

Keyword

nonn,more,hard

Author

Derek Orr, Nov 26 2014

Status

approved