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 A285068 Denominators of the generalized Bernoulli numbers B[3,1] = 3^n*B(n, 1/3). 7
 1, 2, 2, 1, 10, 1, 14, 1, 10, 1, 22, 1, 910, 1, 2, 1, 170, 1, 266, 1, 110, 1, 46, 1, 910, 1, 2, 1, 290, 1, 4774, 1, 170, 1, 2, 1, 639730, 1, 2, 1, 4510, 1, 602, 1, 230, 1, 94, 1, 15470, 1, 22 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The numerators are given in A157799. Because B(n, 2/3) = (-1)^n*B(n, 1/3) (from the e.g.f. z*exp(x*z)/(exp(z)-1) of Bernoulli polynomials {B(n, x)}_{n>=0}) one has for the numbers B[3,2](n) = 3^n*B(n, 2/3) the numerators (-1)^n*A157799(n) and the denominators a(n). This sequence gives also the denominators of {3^n*B(n)}_{n>=0} with numerators given in A285863. LINKS Indranil Ghosh, Table of n, a(n) for n = 0..500 Wolfdieter Lang, On Sums of Powers of Arithmetic Progressions, and Generalized Stirling, Eulerian and Bernoulli numbers, arXiv:1707.04451 [math.NT], 2017. Peter Luschny, Generalized Bernoulli numbers. FORMULA a(n) = denominator(r(n)) with the rationals (in lowest terms) r(n) = Sum_{k=0..n} ((-1)^k / (k+1))*A282629(n, k)*k! = Sum_{k=0..n} ((-1)^k/(k+1))*A284861(n, k). r(n) = B[3,1](n) = 3^n*B(n, 1/3) with the Bernoulli polynomials A196838/A196839 or A053382/A053383. a(n) = A157800(n)/3^n, n >= 0. EXAMPLE The Bernoulli numbers r(n) = B[3,1](n) begin: 1, -1/2, -1/2, 1, 13/10, -5, -121/14, 49, 1093/10, -809, -49205/22, 20317, 61203943/910, -722813, -5580127/2, 34607305, ... The Bernoulli numbers B(3,2](n) begin: 1, 1/2, -1/2, -1, 13/10, 5, -121/14, -49, 1093/10, 809, -49205/22, -20317, 61203943/910, 722813, -5580127/2, -34607305, ... From Peter Luschny, Mar 26 2021: (Start) The generalized Bernoulli numbers as given in the Luschny link are different. 1, -7/2, 23/2, -35, 973/10, -245, 7943/14, -1295, 31813/10, -7721, 288715/22, -13475, 128296423/910, -882557, -4891999/2, 33870025, ...The numerators of these numbers are in A157811. (End) MATHEMATICA Table[Denominator[3^n*BernoulliB[n, 1/3]], {n, 0, 100}] (* Indranil Ghosh, Jul 18 2017 *) PROG (Python) from sympy import bernoulli, Rational def a(n): return (3**n * bernoulli(n, Rational(1, 3))).as_numer_denom()[1] print([a(n) for n in range(101)]) # Indranil Ghosh, Jul 18 2017 (SageMath) # uses [gen_bernoulli_number from A157811] print([denominator((-1)^n*gen_bernoulli_number(n, 3)) for n in range(23)]) # Peter Luschny, Mar 26 2021 (PARI) a(n) = denominator(3^n * bernfrac(n)); \\ Ruud H.G. van Tol, Jan 31 2024 CROSSREFS Cf. A053382/A053383, A157799, A157800, A196838/A196839, A282629, A284861, A285863. Cf. A144845, A157811. Sequence in context: A291082 A295855 A364371 * A306149 A134896 A105620 Adjacent sequences: A285065 A285066 A285067 * A285069 A285070 A285071 KEYWORD nonn,easy,frac AUTHOR Wolfdieter Lang, Apr 28 2017 STATUS approved

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