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a(n) = floor((n^2+n)^(3/2)-n^3).
1

%I #11 Jul 08 2017 12:48:30

%S 1,6,14,25,39,56,76,98,124,153,185,220,258,299,343,389,439,492,548,

%T 607,669,734,802,872,946,1023,1103,1186,1272,1361,1453,1547,1645,1746,

%U 1850,1957,2067,2180,2296,2414,2536,2661,2789,2920,3054,3191,3331,3473,3619,3768,3920,4075,4233,4394

%N a(n) = floor((n^2+n)^(3/2)-n^3).

%H G. C. Greubel, <a href="/A185594/b185594.txt">Table of n, a(n) for n = 1..5000</a>

%t Table[Floor[(n^2+n)^(3/2)]-n^3,{n,1,80}]

%o (PARI) for(n=1,50, print1(floor((n^2+n)^(3/2)-n^3), ", ")) \\ _G. C. Greubel_, Jul 08 2017

%K nonn

%O 1,2

%A _Clark Kimberling_, Jan 31 2011