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A006233
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Denominators of Cauchy numbers of first type.
(Formerly M1558)
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36
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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;
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history;
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internal format)
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OFFSET
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0,2
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COMMENTS
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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.
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REFERENCES
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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).
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LINKS
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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.
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FORMULA
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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
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EXAMPLE
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1, 1/2, -1/6, 1/4, -19/30, 9/4, -863/84, 1375/24, -33953/90,...
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MAPLE
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seq(denom(add(stirling1(n, k)/(k+1), k=0..n)), n=0..12); # Peter Luschny, Apr 28 2009
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MATHEMATICA
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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-François 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 *)
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PROG
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(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
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CROSSREFS
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Cf. A006232, A002206, A002207, A002208, A002209, A002657, A002790.
Sequence in context: A039656 A263326 A226532 * A164020 A326579 A057643
Adjacent sequences: A006230 A006231 A006232 * A006234 A006235 A006236
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KEYWORD
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nonn,frac,nice,easy
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AUTHOR
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N. J. A. Sloane
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STATUS
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approved
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