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 A195016 #33 Feb 09 2024 07:44:49
%S A195016 0,7,17,34,54,81,111,148,188,235,285,342,402,469,539,616,696,783,873,
%T A195016 970,1070,1177,1287,1404,1524,1651,1781,1918,2058,2205,2355,2512,2672,
%U A195016 2839,3009,3186,3366,3553,3743,3940,4140,4347,4557,4774,4994
%N A195016 a(n) = (n*(5*n+7)-(-1)^n+1)/2.
%C A195016 Sequence found by reading the line from 0, in the direction 0, 7,..., and the same line from 0, in the direction 0, 17,..., in the square spiral whose edges have length A195013 and whose vertices are the numbers A195014. Axis perpendicular to the main axis A195015 in the same spiral.
%C A195016 Also sequence found by reading the line from 0, in the direction 0, 7,..., and the same line from 0, in the direction 0, 17,..., in the square spiral whose vertices are the generalized heptagonal numbers A085787. This line is parallel to A153126 in the same spiral.
%H A195016 Vincenzo Librandi, <a href="/A195016/b195016.txt">Table of n, a(n) for n = 0..10000</a>
%H A195016 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1).
%F A195016 n*(10*n-3), if n >= 1, and (2*n+1)*(5*n+1)-1, if n >= 0, interleaved.
%F A195016 G.f.: x*(7+3*x)/((1+x)*(1-x)^3). - _Bruno Berselli_, Oct 14 2011
%t A195016 LinearRecurrence[{2, 0, -2, 1}, {0, 7, 17, 34}, 50] (* _Paolo Xausa_, Feb 09 2024 *)
%o A195016 (Magma) &cat[[n*t,(n+1)*t] where t is 10*n+7: n in [0..22]]; // _Bruno Berselli_, Oct 14 2011
%Y A195016 Cf. A000566, A005476, A028895, A033571, A085787, A152965, A153126, A195013, A195014, A195015.
%K A195016 nonn,easy
%O A195016 0,2
%A A195016 _Omar E. Pol_, Sep 26 2011
%E A195016 Concise definition by _Bruno Berselli_, Oct 14 2011