This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A239831 #23 Sep 08 2022 08:46:07
%S A239831 5,19,39,67,101,143,191,247,308,379,454,539,628,727,830,942,1060,1186,
%T A239831 1318,1458,1604,1758,1917,2086,2259,2442,2629,2826,3027,3237,3453,
%U A239831 3677,3907,4145,4389,4641,4898,5165,5436,5717,6002,6297,6596,6904,7218,7540
%N A239831 Floor(7n^2/2) + floor(5n/2) + floor(3n/7).
%C A239831 This is a quadratic sequence.
%H A239831 Vincenzo Librandi, <a href="/A239831/b239831.txt">Table of n, a(n) for n = 1..1000</a>
%H A239831 Wolfram Alpha, <a href="https://www.wolframalpha.com/share/clip?f=d41d8cd98f00b204e9800998ecf8427e8mn5b969d6">Table of floor(7n^2/2) + floor(5n/2) + floor(3n/7)</a>.
%H A239831 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1,0,0,0,1,-1,-1,1).
%F A239831 a(n) = (n(7n + 5) + (-1)^n - 1)/2 + A132270(3n + 1). [_Bruno Berselli_, Mar 28 2014]
%F A239831 a(n) = +a(n-1) +a(n-2) -a(n-3) +a(n-7) -a(n-8) -a(n-9) +a(n-10). [_Bruno Berselli_, Mar 28 2014]
%e A239831 For n=3, a(3) = floor(7*3^2/2) + floor(5*3/2) + floor(3*3/7) = 39.
%p A239831 A239831:=n->floor(7*n^2/2) + floor(5*n/2) + floor(3*n/7); seq(A239831(n), n=1..50); # _Wesley Ivan Hurt_, Mar 28 2014
%t A239831 Table[Floor[7 n^2/2] + Floor[5 n/2] + Floor[3 n/7], {n, 50}] (* _Bruno Berselli_, Mar 28 2014 *)
%o A239831 (Magma) [Floor(7*n^2/2) + Floor(5*n/2) + Floor(3*n/7): n in [1..50]]; // _Vincenzo Librandi_, Mar 29 2014
%K A239831 nonn,easy
%O A239831 1,1
%A A239831 _Katherine Guo_, Mar 27 2014
%E A239831 More terms from _Bruno Berselli_, Mar 28 2014