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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
I. S. Gradsteyna and I. M. Ryzhik, Table of integrals, series and products, (1980), page 2 (formula 0.131).
Rui-Li Liu and Feng-Zhen Zhao, Log-concavity of two sequences related to Cauchy numbers of two kinds, Online Journal of Analytic Combinatorics, Issue 14 (2019), #09.
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/(2*n) - 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-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 *)
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
print(0, 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 += 1 # A.H.M. Smeets, Nov 14 2018
(Python)
from fractions import Fraction
from sympy.functions.combinatorial.numbers import stirling
def A006233(n): return sum(Fraction(stirling(n, k, kind=1, signed=True), k+1) for k in range(n+1)).denominator # Chai Wah Wu, Jul 09 2023
CROSSREFS
Sequence in context: A263326 A226532 A335049 * A164020 A326579 A057643
KEYWORD
nonn,frac,nice,easy
AUTHOR
STATUS
approved

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Last modified February 27 12:56 EST 2024. Contains 370375 sequences. (Running on oeis4.)