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A006233 Denominators of Cauchy numbers of first type.
(Formerly M1558)
36
1, 2, 6, 4, 30, 4, 84, 24, 90, 20, 132, 8, 5460, 840, 360, 48, 1530, 4, 1596, 168, 1980, 1320, 8280, 80, 81900, 6552, 1512, 112, 3480, 80, 114576, 7392, 117810, 7140, 1260, 8, 3838380, 5928, 936, 48, 81180, 440, 1191960, 55440, 869400, 38640, 236880, 224 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The corresponding numerators are given in A006232.

The signed rationals A006232(n)/a(n) provide the a-sequence for the Stirling2 Sheffer matrix A048993. See the W. Lang link concerning Sheffer a- and z-sequences.

Cauchy numbers of the first type are also called Bernoulli numbers of the second kind.

REFERENCES

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 294.

H. Jeffreys and B. S. Jeffreys, Methods of Mathematical Physics, Cambridge, 1946, p. 259.

L. Jolley, Summation of Series, Chapman and Hall, London, 1925, pp. 14-15 (formula 70).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

T. D. Noe, Table of n, a(n) for n = 0..1000

A. Adelberg, 2-adic congruences of Norland numbers and of Bernoulli numbers of the second kind, J. Number Theory, 73 (1998), 47-58.

I. S. Gradsteyn, I. M. Ryzhik, Table of integrals, series and products, (1980), page 2 (formula 0.131).

W. Lang, Sheffer a- and z-sequences

Donatella Merlini, Renzo Sprugnoli and M. Cecilia Verri, The Cauchy numbers, Discrete Math. 306 (2006), no. 16, 1906-1920.

Eric Weisstein's World of Mathematics, Bernoulli Number of the Second Kind

Ming Wu and Hao Pan, Sums of products of Bernoulli numbers of the second kind, Fib. Quart., 45 (2007), 146-150.

Feng-Zhen Zhao, Sums of products of Cauchy numbers, Discrete Math., 309 (2009), 3830-3842.

FORMULA

Denominator of integral of x(x-1)...(x-n+1) from 0 to 1.

E.g.f.: x/log(1+x).

Denominator of Sum_{k=0..n} A048994(n,k)/(k+1). [Peter Luschny, Apr 28 2009]

a(n) = denominator(f(n) * n!), where f(0) = 1, f(n) = Sum_{k=0..n-1} (-1)^(n-k+1) * f(k) / (n-k+1). - Daniel Suteu, Feb 23 2018

Sum_{k = 1..n} (1/k) = A001620 + log(n) + 1/(2n) - Sum_{k >= 2} abs((A006232(k)/a(k)/k/(Product_{j = 0..k-1} (n-j)))), (see I. S. Gradsteyn, I. M. Ryzhik). - A.H.M. Smeets, Nov 14 2018

EXAMPLE

1, 1/2, -1/6, 1/4, -19/30, 9/4, -863/84, 1375/24, -33953/90,...

MAPLE

seq(denom(add(stirling1(n, k)/(k+1), k=0..n)), n=0..12); # Peter Luschny, Apr 28 2009

MATHEMATICA

With[{nn=50}, Denominator[CoefficientList[Series[x/Log[1+x], {x, 0, nn}], x] Range[0, nn]!]] (* Harvey P. Dale, Oct 28 2011 *)

a[n_] := Sum[ StirlingS1[n, k]/(k+1), {k, 0, n}] // Denominator; Table[a[n], {n, 0, 40}] (* Jean-Fran├žois Alcover, Jan 10 2013, after Peter Luschny *)

Join[{1}, Array[Abs@Denominator[ Integrate[Product[(x - k), {k, 0, # - 1}], {x, 0, 1}]] &, 50]] (* Michael De Vlieger, Nov 13 2018 *)

PROG

(PARI) for(n=0, 50, print1(denominator( sum(k=0, n, stirling(n, k, 1)/(k+1)) ), ", ")) \\ G. C. Greubel, Nov 13 2018

(MAGMA) [Denominator((&+[StirlingFirst(n, k)/(k+1): k in [0..n]])): n in [0..50]]; // G. C. Greubel, Nov 13 2018

(Sage)

def A006233_list(len):

    f, R, C = 1, [1], [1]+[0]*(len-1)

    for n in (1..len-1):

        for k in range(n, 0, -1):

            C[k] = -C[k-1] * k / (k + 1)

        C[0] = -sum(C[k] for k in (1..n))

        R.append((C[0]*f).denominator())

        f *= n+1

    return R

print A006233_list(50)  # G. C. Greubel, Nov 13 2018

(Python) Results are abs values

from fractions import gcd

aa, n, sden = [0, 1], 1, 1

while n < 20:

....j, snom, sden, a = 1, 0, (n+1)*sden, 0

....while j < len(aa):

........snom, j = snom+aa[j]*(sden//(j+1)), j+1

....nom, den = snom, sden

....print(n, den//gcd(nom, den))

....aa, j = aa+[-aa[j-1]], j-1

....while j > 0:

........aa[j], j = n*aa[j]-aa[j-1], j-1

....n = n+1 # A.H.M. Smeets, Nov 14 2018

CROSSREFS

Cf. A006232, A002206, A002207, A002208, A002209, A002657, A002790.

Sequence in context: A039656 A263326 A226532 * A164020 A057643 A073039

Adjacent sequences:  A006230 A006231 A006232 * A006234 A006235 A006236

KEYWORD

nonn,frac,nice,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified December 15 21:01 EST 2018. Contains 318154 sequences. (Running on oeis4.)