a(n) counts different values of i^2+j^2+k^2 <= n^2 or number of distances from the origin to all integer points inside a sphere of radius n.
1, 2, 5, 9, 15, 23, 32, 43, 55, 70, 86, 103, 122, 143, 166, 190, 215, 243, 273, 304, 336
1 seqfan posts
Mon Nov 2 01:54:51 CET 2009 [seqfan] Re: Incongruous reordering of N