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a(n) = floor(n^2/Pi).
2

%I #23 Mar 09 2022 16:46:08

%S 0,0,1,2,5,7,11,15,20,25,31,38,45,53,62,71,81,91,103,114,127,140,154,

%T 168,183,198,215,232,249,267,286,305,325,346,367,389,412,435,459,484,

%U 509,535,561,588,616,644,673,703,733,764,795,827,860,894

%N a(n) = floor(n^2/Pi).

%F a(n) = A032615(n^2). - _Michel Marcus_, Jan 30 2022

%t a[n_]:=Floor[(n^2)/Pi]; (* _Vladimir Joseph Stephan Orlovsky_, Dec 12 2008 *)

%o (PARI) a(n) = n^2\Pi; \\ _Michel Marcus_, Jan 30 2022

%o (Python) from math import pi

%o print([int(n**2/pi) for n in range(54)]) # _Karl-Heinz Hofmann_, Feb 01 2022

%Y Cf. A032615.

%K nonn,easy

%O 0,4

%A _Patrick De Geest_, May 15 1998