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 A118348 #7 Mar 17 2021 22:51:20
%S A118348 1,3,18,121,873,6606,51728,415629,3407391,28388847,239675406,
%T A118348 2045980440,17629939980,153142537440,1339599358944,11789960853293,
%U A118348 104327344928619,927627432162129,8283625668834238,74259685465582569,668054892245119353
%N A118348 Semi-diagonal (two rows below central terms) of pendular triangle A118345 and equal to the self-convolution cube of the central terms (A118346).
%H A118348 G. C. Greubel, <a href="/A118348/b118348.txt">Table of n, a(n) for n = 0..500</a>
%F A118348 G.f.: ( series_inverse( x*(1-2*x +sqrt((1-2*x)*(1-6*x)))/(2*(1-2*x)) )/x )^3.
%t A118348 CoefficientList[(InverseSeries[Series[x*(1-2*x +Sqrt[(1-2*x)*(1-6*x)])/(2*(1-2*x)), {x, 0, 30}]]/x)^3, x] (* _G. C. Greubel_, Mar 17 2021 *)
%o A118348 (PARI) {a(n) = polcoeff( (serreverse(x*(1-2*x+sqrt((1-2*x)*(1-6*x)+x*O(x^n)))/(2*(1-2*x)))/x)^3, n)}
%o A118348 (Sage)
%o A118348 def A118347_list(prec):
%o A118348 P.<x> = PowerSeriesRing(ZZ, prec)
%o A118348 return P( (( x*(1-2*x +sqrt((1-2*x)*(1-6*x)))/(2*(1-2*x)) ).reverse()/x)^3 ).list()
%o A118348 A118347_list(31) # _G. C. Greubel_, Mar 17 2021
%o A118348 (Magma)
%o A118348 R<x>:=PowerSeriesRing(Rationals(), 30);
%o A118348 Coefficients(R!( (Reversion( x*(1-2*x +Sqrt((1-2*x)*(1-6*x)))/(2*(1-2*x)) )/x)^3 )); // _G. C. Greubel_, Mar 17 2021
%Y A118348 Cf. A118345, A118346, A118347, A118349.
%K A118348 nonn
%O A118348 0,2
%A A118348 _Paul D. Hanna_, Apr 26 2006