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 A290159 #16 Jul 25 2017 20:15:21
%S A290159 1,1,3,-3,3,15,-57,21,867,-1893,1581,8283,-76953,34203,361551,-869691,
%T A290159 6420387,34130067,-167946159,79445631,1696170093,-4239570255,
%U A290159 4083041217,21859150803,-442212416121,215805655695,2316081934929,-5909439428697,11656013746863,62663656767603,-322045194694305,160129270032933,27589357112530467
%N A290159 Numerators of coefficients in Taylor series expansion of (1+x+x^2)^(1/2).
%C A290159 Denominators of the Taylor series expansion are given by A046161.
%C A290159 The terms after the second are divisible by 3.
%C A290159 The sequence of the absolute values is not monotonic.
%p A290159 a:= n-> numer(coeff(series(sqrt(1+x+x^2), x, n+3), x, n)):
%p A290159 seq(a(n), n=0..35); # _Alois P. Heinz_, Jul 25 2017
%t A290159 Numerator[CoefficientList[Series[Sqrt[1+x+x^2], {x, 0, 32}], x]]
%o A290159 (PARI) x = 'x + O('x^40); apply(x->numerator(x), Vec((1+x+x^2)^(1/2))) \\ _Michel Marcus_, Jul 24 2017
%Y A290159 Cf. A046161 (denominators).
%K A290159 sign,frac
%O A290159 0,3
%A A290159 _Bruno Zürcher_, Jul 22 2017