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 A225566 #25 Jun 02 2025 08:34:32
%S A225566 2,4,6,12,18,24,36,48,60,80,100,120,150,180,210,252,294,336,392,448,
%T A225566 504,576,648,720,810,900,990,1100,1210,1320,1452,1584,1716,1872,2028,
%U A225566 2184,2366,2548,2730,2940,3150,3360,3600,3840,4080,4352,4624,4896,5202,5508,5814,6156,6498,6840,7220,7600,7980,8400,8820,9240,9702
%N A225566 The set of magic numbers for an idealized harmonic oscillator atomic nucleus with a biaxially deformed prolate ellipsoid shape and an oscillator ratio of 3:1.
%C A225566 Partial sums of series of three doubled triangular numbers of the same value in order: 2,2,2,6,6,6,12,12,12,20,20,20... (cf. A002378).
%H A225566 Harvey P. Dale, <a href="/A225566/b225566.txt">Table of n, a(n) for n = 1..1000</a>
%H A225566 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,2,-4,2,-1,2,-1).
%F A225566 From _Colin Barker_, Oct 01 2016: (Start)
%F A225566 a(n) = 2*a(n-1)-a(n-2)+2*a(n-3)-4*a(n-4)+2*a(n-5)-a(n-6)+2*a(n-7)-a(n-8) for n>8.
%F A225566 G.f.: 2*x / ((1-x)^4*(1+x+x^2)^2).
%F A225566 (End)
%t A225566 Accumulate[Flatten[{#,#,#}&/@Accumulate[2*Range[30]]]] (* _Harvey P. Dale_, May 01 2014 *)
%o A225566 (PARI) Vec(2*x/((1-x)^4*(1+x+x^2)^2) + O(x^60)) \\ _Colin Barker_, Oct 01 2016
%Y A225566 Equals twice A144677. Cf. A002378.
%K A225566 nonn,easy
%O A225566 1,1
%A A225566 _Jess Tauber_, May 14 2013
%E A225566 More terms from _N. J. A. Sloane_, May 17 2013