Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #26 Oct 26 2020 08:05:53
%S 0,1,2,2,3,3,2,2,3,3,4,4,3,3,4,4,5,3,4,4,4,3,4,4,4,3,4,4,4,3,4,4,4,3,
%T 4,4,4,3,4,4,4,3,4,4,4,3,4,4,4,3,4,4,4,3,4,4,4,3,4,4,4,3,4,4,4,3,4,4,
%U 4,3,4,4,4,3,4,4,4,3,4,4,4,3,4,4,4,3,4
%N a(n) is the number of zeros of the Bernoulli B(n, x) polynomial in the open interval (-1, +1).
%C The n-th Bernoulli polynomial is defined by the exponential generating function: t*exp(x*t)/(exp(t)-1) = Sum_{n>=0} bernoulli(n,x)/n!*t^n.
%C The first few Bernoulli polynomials are:
%C B(0,x) = 1
%C B(1,x) = x - 1/2
%C B(2,x) = x^2 - x + 1/6
%C B(3,x) = x^3 - 3/2 x^2 + 1/2 x
%C B(4,x) = x^4 - 2x^3 + x^2 - 1/30
%C Conjecture 1: for n > 32, a(n) = 3 for n odd and a(n) = 4 otherwise.
%C Conjecture 2: A284849(n) - a(n) > 0 if n = 6, 7,...,15 and n = 17.
%C Conjecture 1 is false. It appears that for n => 13, a(n) = 3 for n == 1 (mod 4) and a(n) = 4 otherwise. - _Robert Israel_, May 29 2017
%H A. P. Veselov and J. P. Ward, <a href="https://doi.org/10.1016/j.jmaa.2004.12.046">On the real zeros of the Hurwitz zeta-function and Bernoulli polynomials</a>, Journal of Mathematical Analysis and Applications 305 (2005), 712-721.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/BernoulliPolynomial.html">Bernoulli Polynomial</a>
%F Conjectures from _Colin Barker_, Jan 22 2020: (Start)
%F G.f.: x*(1 + 2*x + 2*x^2 + 3*x^3 + 2*x^4 + 2*x^9 + 2*x^10 + 2*x^15 - x^19) / ((1 - x)*(1 + x)*(1 + x^2)).
%F a(n) = a(n-4) for n>16.
%F (End)
%e a(6) = 2 because the zeros of B(6,x) = x^6 - 3x^5 + 5/2 x^4 - 1/2 x^2 + 1/42 are:
%e x1 = -0.2728865...-0.06497293...*i,
%e x2 = -0.2728865...+0.06497293...*i,
%e x3 = 0.2475407...,
%e x4 = 0.7524592...,
%e x5 = 1.272886...-.06497293...*i,
%e x6 = 1.272886...+.06497293...*i
%e with two roots x3 and x4 in the open interval (-1, +1).
%p f:= proc(n) sturm(sturmseq(bernoulli(n,x),x),x,-1,1) - `if`(n::odd and n > 1, 1, 0) end proc:
%p map(f, [$0..100]); # _Robert Israel_, May 29 2017
%t a[n_] := NSolve[-1 < x < 1 && BernoulliB[n, x] == 0, x, Reals, WorkingPrecision -> 100] // Length;
%t a /@ Range[0, 100] (* _Jean-François Alcover_, Oct 26 2020 *)
%Y Cf. A284849.
%K nonn
%O 0,3
%A _Michel Lagneau_, May 22 2017
%E Corrected by _Robert Israel_, May 29 2017