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 A195030 #41 Oct 23 2024 14:47:18
%S A195030 0,1,2,3,34,93,180,295,438,609,808,1035,1290,1573,1884,2223,2590,2985,
%T A195030 3408,3859,4338,4845,5380,5943,6534,7153,7800,8475,9178,9909,10668,
%U A195030 11455,12270,13113,13984,14883,15810,16765,17748,18759,19798,20865,21960,23083
%N A195030 a(n) = (n-2)*(14*n-39) for n > 2, otherwise a(n) = n.
%C A195030 Union of [1, 2] and A195021.
%C A195030 Sequence found by reading the line from 0, in the direction 0, 1,..., in the Pythagorean spiral whose edges have length A195019 and whose vertices are the numbers A195020. This is the one of the semi-axis of the square spiral, which is related to the primitive Pythagorean triple [3, 4, 5].
%H A195030 Vincenzo Librandi, <a href="/A195030/b195030.txt">Table of n, a(n) for n = 0..1000</a>
%H A195030 Bruno Berselli, <a href="http://www.base5forum.it/upload/A195030.jpg">Illustration of initial terms: An origin of A195030</a>
%H A195030 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A195030 G.f.: x*(1-x+30*x^3-2*x^4)/(1-x)^3. - _Bruno Berselli_, Oct 18 2011
%t A195030 Join[{0,1,2},Table[(n-2)*(14*n-39),{n,3,50}]] (* _Vincenzo Librandi_, Jul 10 2012 *)
%o A195030 (Magma) [0,1,2] cat[(n-2)*(14*n-39): n in [3..50]]; // _Vincenzo Librandi_, Jul 10 2012
%o A195030 (PARI) a(n)=if(n,([0,1,0; 0,0,1; 1,-3,3]^n*[0;1;2])[1,1],0) \\ _Charles R Greathouse IV_, Oct 16 2015
%Y A195030 Cf. A195019, A195020, A195021, A185019, A193053, A198017.
%K A195030 nonn,easy
%O A195030 0,3
%A A195030 _Omar E. Pol_, Oct 18 2011
%E A195030 Both sequence (based on A195021) and definition suggested by _Bruno Berselli_, Oct 18 2011