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 A122973 #15 Oct 17 2016 10:06:16
%S A122973 1,12,42,162,642,2562,10242,40962,163842,655362,2621442,10485762,
%T A122973 41943042,167772162,671088642,2684354562,10737418242,42949672962,
%U A122973 171798691842,687194767362,2748779069442,10995116277762,43980465111042,175921860444162,703687441776642
%N A122973 Number of vertices on the surface of an icosahedron.
%H A122973 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (5,-4).
%F A122973 a(n) = 1 if n=0, 10*4^(n-1)+2 otherwise.
%F A122973 G.f.: 1-6*x*(-2+3*x) / ( (4*x-1)*(x-1) ). - _R. J. Mathar_, Feb 02 2011
%F A122973 For a(n)>1: a(1)=12, a(2)=42, a(n) = 5*a(n-1)-4*a(n-2). [_Harvey P. Dale_, May 05 2011]
%t A122973 Join[{1},LinearRecurrence[{5,-4},{12,42},30]] (* or *) CoefficientList[ Series[1-6x (-2+3x)/((4x-1)(x-1)),{x,0,30}],x] (* _Harvey P. Dale_, May 05 2011 *)
%Y A122973 Cf. A005901.
%K A122973 nonn,easy
%O A122973 0,2
%A A122973 Alden Chew (aldenc98(AT)yahoo.com), Oct 27 2006