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%I #9 Nov 19 2021 08:12:30
%S 1,8,4,2,6,2,6,7,1,3,5,8,3,8,1,3,5,9,3,9,6,7,5,7,0,6,1,7,5,4,4,3,4,2,
%T 2,0,8,7,4,9,6,7,6,0,1,5,2,1,6,3,5,1,3,5,1,5,6,7,5,5,5,0,9,9,2,2,2,2,
%U 0,1,6,6,6,2,7,9,1,8,9,0,1,6,4,5,0,1,8,1,6
%N Decimal expansion of the positive real root of x^4 - 3*x - 6.
%C This constant appears in the upper bounds formula of the peak sidelobe level of Rudin-Shapiro sequences.
%H Tom Høholdt, Helge Elbrønd Jensen and Jørn Justesen, <a href="https://doi.org/10.1109/TIT.1985.1057071">Aperiodic correlations and the merit factor of a class of binary sequences (Corresp.)</a>, in IEEE Transactions on Information Theory, vol. 31, no. 4, pp. 549-552, July 1985; on <a href="https://www.researchgate.net/publication/3084194_Aperiodic_correlations_and_the_merit_factor_of_a_class_of_binary_sequences_Corresp">Research Gate</a>.
%H Daniel J. Katz and Courtney M. van der Linden, <a href="https://arxiv.org/abs/2108.07318">Peak Sidelobe Level and Peak Crosscorrelation of Golay-Rudin-Shapiro Sequences</a>, arXiv:2108.07318 [cs.IT], 2021. See Theorem 1.2, p. 4.
%H Stefano Spezia, <a href="/A348908/a348908.jpg">Exact form of the constant</a>
%F See the formula in Links section.
%e 1.8426267135838135939675706175443422...
%t First[RealDigits[N[Root[x^4-3x-6,x,2],89]]]
%o (PARI) solve(x=0, 2, x^4 - 3*x - 6) \\ _Michel Marcus_, Nov 03 2021
%Y Cf. A020985, A020987, A348909.
%K nonn,cons
%O 1,2
%A _Stefano Spezia_, Nov 03 2021