[seqfan] Help, please

Richard Guy rkg at cpsc.ucalgary.ca
Tue Apr 20 21:53:45 CEST 2010


I'm sure that this sequence is in OEIS, but
I'm not a good looker, and I've probably
made mistakes.

Number of edges in the graph on  n  vertices,
1, 2, 3, ..., n,  where two vertces are
joined just if their label sum to a perfect
square.

a(1) = 0, 0, 1, 1, 2, 3, 4, 5, 6, 7, 8, 9,
11, 13, 15, 16,

E.g., for  n = 7 the graph contains the 4 edges
1-3, 2-7, 3-6, 4-5.

For extra credit: what is the size of  a(n),
asymptotically?

Thanks in anticipation of help.   R.




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