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 A027913 #25 Nov 22 2020 01:24:05
%S A027913 1,1,2,3,10,15,50,77,266,414,1452,2277,8074,12727,45474,71955,258570,
%T A027913 410346,1481108,2355962,8533660,13599915,49402850,78855339,287134346,
%U A027913 458917850,1674425300,2679183405,9792273690,15683407785
%N A027913 T(n,[ n/2 ]), T given by A027907.
%C A027913 The median coefficient in the expansion of (1 + x + x^2)^n. - _Vladimir Reshetnikov_, Nov 21 2020
%H A027913 Robert Israel, <a href="/A027913/b027913.txt">Table of n, a(n) for n = 0..2550</a>
%F A027913 a(n) = GegenbauerC(floor(n/2), -n, -1/2). - _Emanuele Munarini_, Oct 18 2016
%F A027913 G.f.: g(t) = (1+(t+t^2)*A(t^2)+t^4*A(t^2)^2)/(1-t^2*A(t^2)-3*t^4*A(t^2)^2), where A(t) is the g.f. of A143927 and satisfies A(t) = [1 + x*A(t) + t^2*A(t)^2]^2. - _Emanuele Munarini_, Oct 20 2016
%p A027913 seq(simplify(GegenbauerC(floor(n/2),-n,-1/2)), n=0..100); # _Robert Israel_, Oct 20 2016
%t A027913 Table[GegenbauerC[Floor[n/2], -n, -1/2] + KroneckerDelta[n, 0], {n, 0,
%t A027913 100}] (* _Emanuele Munarini_, Oct 20 2016 *)
%o A027913 (Maxima) makelist(ultraspherical(floor(n/2),-n,-1/2),n,0,12); /* _Emanuele Munarini_, Oct 18 2016 */
%Y A027913 Cf. A027907, A027908.
%K A027913 nonn
%O A027913 0,3
%A A027913 _Clark Kimberling_