A033469 -id:A033469 - cp's OEIS frontend

A001896 Numerators of cosecant numbers -2(2^(2n - 1) - 1)Bernoulli(2n); also of Bernoulli(2n, 1/2) and Bernoulli(2n, 1/4).

1, -1, 7, -31, 127, -2555, 1414477, -57337, 118518239, -5749691557, 91546277357, -1792042792463, 1982765468311237, -286994504449393, 3187598676787461083, -4625594554880206790555, 16555640865486520478399, -22142170099387402072897

Offset: 0

N. J. A. Sloane

|A001896(n)|*Pi^(2n)/A001897(n) is the value of the multi zeta function z(2,2,...,2) with n 2's, where z(k_l,k_2,...,k_n) = Sum_{i_n >= i_(n-1) >= ... >= i_1 >= 1}1/((i_1)^k_1 (i_2)^k_2 ... (i_n)^k_n). The proof is simple: start with the product expansion sin(Pi x)/(Pi x) = Product_{r>=1}(1-x^2/r^2), take reciprocals, and expand the right side. The coefficient of x^(2n) is seen to be z(2,2,...,2) with n 2's. - David Callan, Aug 27 2014

See A062715 for a method of obtaining the cosecant numbers from the square of Pascal's triangle. - Peter Bala, Jul 18 2013

			1, -1/12, 7/240, -31/1344, 127/3840, -2555/33792, 1414477/5591040, -57337/49152, 118518239/16711680, ... = a(n)/A033469(n).
Cosecant numbers {-2*(2^(2*n-1)-1)*Bernoulli(2*n)} are 1, -1/3, 7/15, -31/21, 127/15, -2555/33, 1414477/1365, -57337/3, 118518239/255, -5749691557/399, 91546277357/165, -1792042792463/69, 1982765468311237/1365, -286994504449393/3, 3187598676787461083/435, ... = a(n)/A001897(n).

H. T. Davis, Tables of the Mathematical Functions. Vols. 1 and 2, 2nd ed., 1963, Vol. 3 (with V. J. Fisher), 1962; Principia Press of Trinity Univ., San Antonio, TX, Vol. 2, p. 187.
S. A. Joffe, Sums of like powers of natural numbers, Quart. J. Pure Appl. Math. 46 (1914), 33-51.
N. E. Nörlund, Vorlesungen über Differenzenrechnung. Springer-Verlag, Berlin, 1924, p. 458.
J. Riordan, Combinatorial Identities, Wiley, 1968, p. 199. See Table 3.3.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Hector Blandin and Rafael Diaz, Compositional Bernoulli numbers, arXiv:0708.0809 [math.CO], 2007-2008; Page 7, 3rd table, (B^sin)_1,n is identical to |A001896| / A001897.
S. A. Joffe, Sums of like powers of natural numbers, Quart. J. Pure Appl. Math. 46 (1914), 33-51. [Annotated scanned copy of pages 38-51 only, plus notes]
Masanobu Kaneko, Maneka Pallewatta, and Hirofumi Tsumura, On Polycosecant Numbers, J. Integer Seq. 23 (2020), no. 6, 17 pp. See line k=1 of Table 1 p. 3.
D. H. Lehmer, Lacunary recurrence formulas for the numbers of Bernoulli and Euler, Annals Math., 36 (1935), 637-649.
N. E. Nörlund, Vorlesungen über Differenzenrechnung, Springer-Verlag, Berlin, 1924 [Annotated scanned copy of pages 144-151 and 456-463]
Index entries for sequences related to Bernoulli numbers.

Cf. A001897 (denominators), A033469, A036280, A062715, A145901.

Cf. A132092-A132099.

seq(numer(bernoulli(2*n, 1/2)), n=0..20);

a[n_] := -2*(2^(2*n-1)-1)*BernoulliB[2*n]; Table[a[n], {n, 0, 20}] // Numerator (* Jean-François Alcover, Sep 11 2013 *)

a(n) = numerator(-2*(2^(2*n-1)-1)*bernfrac(2*n)); \\ Michel Marcus, Mar 01 2015

def A001896_list(len):
    R, C = [1], [1]+[0]*(len-1)
    for n in (1..len-1):
        for k in range(n, 0, -1):
            C[k] = C[k-1] / (8*k*(2*k+1))
        C[0] = -sum(C[k] for k in (1..n))
        R.append((C[0]*factorial(2*n)).numerator())
    return R
A001896_list(18) # Peter Luschny, Feb 20 2016

a(n) = numerator((-Pi^2)^(-n)*Integral_{x=0..1} (log(x/(1-x)))^2*n). - Groux Roland, Nov 10 2009
a(n) = numerator((-1)^(n+1)*(2*Pi)^(-2*n)*(2*n)!*Li_{2*n}(-1)). - Peter Luschny, Jun 29 2012
E.g.f. 2*x*exp(x)/(exp(2*x) - 1) = 1 - 1/3*x^2/2! + 7/15*x^4/4! - 31/21*x^6/6! + .... = Sum_{n >= 0} a(n)/A001897(n)*x^(2*n)/(2*n)!. - Peter Bala, Jul 18 2013
a(n) = numerator((-1)^n*I(n)), where I(n) = 2*Pi*Integral_{z=-oo..oo} (z^n / (exp(-Pi*z) + exp(Pi*z)))^2. - Peter Luschny, Jul 25 2021

A001897 Denominators of cosecant numbers: -2(2^(2n-1)-1)Bernoulli(2n).

Original entry on oeis.org

1, 3, 15, 21, 15, 33, 1365, 3, 255, 399, 165, 69, 1365, 3, 435, 7161, 255, 3, 959595, 3, 6765, 903, 345, 141, 23205, 33, 795, 399, 435, 177, 28393365, 3, 255, 32361, 15, 2343, 70050435, 3, 15, 1659, 115005, 249, 1702155, 3, 30705, 136059, 705, 3, 2250885, 3, 16665, 2163

Offset: 0

N. J. A. Sloane

Same as half the denominators of the even-indexed Bernoulli numbers B_{2*n} for n>0, by the von Staudt-Clausen theorem and Fermat's little theorem. - Bernd C. Kellner and Jonathan Sondow, Jan 02 2017 [This is implemented in the second Maple program. - Peter Luschny, Aug 21 2021]

			Cosecant numbers {-2*(2^(2*n-1)-1)*Bernoulli(2*n)} are 1, -1/3, 7/15, -31/21, 127/15, -2555/33, 1414477/1365, -57337/3, 118518239/255, -5749691557/399, 91546277357/165, -1792042792463/69, 1982765468311237/1365, -286994504449393/3, 3187598676787461083/435, ... = A001896/A001897.

H. T. Davis, Tables of the Mathematical Functions. Vols. 1 and 2, 2nd ed., 1963, Vol. 3 (with V. J. Fisher), 1962; Principia Press of Trinity Univ., San Antonio, TX, Vol. 2, p. 187.
S. A. Joffe, Sums of like powers of natural numbers, Quart. J. Pure Appl. Math. 46 (1914), 33-51.
N. E. Nörlund, Vorlesungen über Differenzenrechnung. Springer-Verlag, Berlin, 1924, p. 458.
J. Riordan, Combinatorial Identities, Wiley, 1968, p. 199. See Table 3.3.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Hector Blandin and Rafael Diaz, Compositional Bernoulli numbers, arXiv:0708.0809 [math.CO], 2007-2008, Page 7, 3rd table, (B^sin)_1,n is identical to |A001896| / A001897.
S. A. Joffe, Sums of like powers of natural numbers, Quart. J. Pure Appl. Math. 46 (1914), 33-51. [Annotated scanned copy of pages 38-51 only, plus notes]
Masanobu Kaneko, Maneka Pallewatta, and Hirofumi Tsumura, On Polycosecant Numbers, J. Integer Seq. 23 (2020), no. 6, 17 pp. See line k=1 of Table 1 p. 3.
D. H. Lehmer, Lacunary recurrence formulas for the numbers of Bernoulli and Euler, Annals Math., 36 (1935), 637-649.
N. E. Nörlund, Vorlesungen über Differenzenrechnung, Springer 1924, p. 27.
N. E. Nörlund, Vorlesungen über Differenzenrechnung, Springer-Verlag, Berlin, 1924 [Annotated scanned copy of pages 144-151 and 456-463]

Cf. A001896 (numerators), A027642, A033469, A160014, A241171, A277087, A340556.

Cf. A132092-A132099,

[Denominator(2*(1-2^(2*n-1))*Bernoulli(2*n)): n in [0..55]]; // G. C. Greubel, Apr 06 2019

b := n -> bernoulli(n)*2^add(i,i=convert(n,base,2));
a := n -> denom(b(2*n)); # Peter Luschny, May 02 2009
# Alternative :
Clausen := proc(n) local i,S; map(i->i+1, numtheory[divisors](n));
S := select(isprime, %); if S <> {} then mul(i,i=S) else NULL fi end:
A001897_list := n -> [1,seq(Clausen(2*i)/2,i=1..n-1)];
A001897_list(52); # Peter Luschny, Oct 03 2011

a[n_] := Denominator[-2*(2^(2*n-1)-1)*BernoulliB[2*n]]; Table[a[n], {n, 0, 55}] (* Jean-François Alcover, Sep 11 2013 *)

a(n) = denominator(-2*(2^(2*n-1)-1)*bernfrac(2*n)); \\ Michel Marcus, Apr 06 2019

def A001897(n):
    if n == 0:
        return 1
    M = (d + 1 for d in divisors(2 * n))
    return prod(s for s in M if is_prime(s)) / 2
[A001897(n) for n in range(55)]  # Peter Luschny, Feb 20 2016

a(0)=1, a(n)=(1/2)*A002445(n) for n>=1. - Joerg Arndt, May 07 2012
a(n) = denominator((2*n)!*Li_{2*n}(1)) for n > 0. - Peter Luschny, Jun 29 2012
a(0)=1, a(n) = (1/2)*A027642(2*n) = (3/2)*A277087(n) for n>=1. - Jonathan Sondow, Dec 14 2016
From Peter Luschny, Sep 06 2017: (Start)
a(n) = denominator(r(n)) where r(n) = Sum_{0..n} (-1)^(n-k)*A241171(n, k)/(2*k+1).
a(n) = denominator(bernoulli(2*n, 1/2))/4^n = A033469(n)/4^n. (End)
Apparently a(n) = denominator(Sum_{k=0..2*n-2} (-1)^k*E2(2*n-1, k+1)/binomial(4*n-1, k+1)), where E2(n, k) denotes the second-order Eulerian numbers A340556. - Peter Luschny, Feb 17 2021

A157780 Denominator of Bernoulli(n, 1/2).

Original entry on oeis.org

1, 1, 12, 1, 240, 1, 1344, 1, 3840, 1, 33792, 1, 5591040, 1, 49152, 1, 16711680, 1, 104595456, 1, 173015040, 1, 289406976, 1, 22900899840, 1, 201326592, 1, 116769423360, 1, 7689065201664, 1, 1095216660480, 1, 51539607552, 1

Offset: 0

N. J. A. Sloane, Nov 08 2009

Included for completeness, A033469 is the official version of this sequence.

Vincenzo Librandi, Table of n, a(n) for n = 0..250

For numerators see A157779.

Table[Denominator[BernoulliB[n, 1/2]], {n, 0, 50}] (* Vincenzo Librandi, Mar 19 2014 *)

a(n) = denominator(-(1-2^(1-n))*Bernoulli(n)). - Fabián Pereyra, Dec 31 2022

A335948 T(n, k) = denominator([x^k] b_n(x)), where b_n(x) = Sum_{k=0..n} binomial(n,k)* Bernoulli(k, 1/2)*x^(n-k). Triangle read by rows, for n >= 0 and 0 <= k <= n.

Original entry on oeis.org

1, 1, 1, 12, 1, 1, 1, 4, 1, 1, 240, 1, 2, 1, 1, 1, 48, 1, 6, 1, 1, 1344, 1, 16, 1, 4, 1, 1, 1, 192, 1, 48, 1, 4, 1, 1, 3840, 1, 48, 1, 24, 1, 3, 1, 1, 1, 1280, 1, 16, 1, 40, 1, 1, 1, 1, 33792, 1, 256, 1, 32, 1, 8, 1, 4, 1, 1, 1, 3072, 1, 256, 1, 32, 1, 8, 1, 12, 1, 1

Offset: 0

Peter Luschny, Jul 01 2020

See A335947 for formulas and references concerning the polynomials.

			First few polynomials are:
b_0(x) = 1;
b_1(x) = x;
b_2(x) = -(1/12) + x^2;
b_3(x) = -(1/4)*x + x^3;
b_4(x) = (7/240) - (1/2)*x^2 + x^4;
b_5(x) = (7/48)*x - (5/6)*x^3 + x^5;
b_6(x) = -(31/1344) + (7/16)*x^2 - (5/4)*x^4 + x^6;
Triangle starts:
1;
1,     1;
12,    1,    1;
1,     4,    1,   1;
240,   1,    2,   1,  1;
1,     48,   1,   6,  1,  1;
1344,  1,    16,  1,  4,  1,  1;
1,     192,  1,   48, 1,  4,  1, 1;
3840,  1,    48,  1,  24, 1,  3, 1, 1;
1,     1280, 1,   16, 1,  40, 1, 1, 1, 1;
33792, 1,    256, 1,  32, 1,  8, 1, 4, 1, 1;

Cf. A335947 (numerators), A157780 (column 0), A033469 (column 0 even indices only).

A335954 a(n) = Numerator(-2nHurwitzZeta(1 - 2*n, -1/2)) for n > 0, and a(0) = 1.

Original entry on oeis.org

1, 11, 127, 221, 367, -1895, 1447237, -57253, 118526399, -5749677193, 91546283957, -1792042789427, 1982765468376757, -286994504449237, 3187598676787485443, -4625594554880206360895, 16555640865486520494719, -22142170099387402072693, 904185845619475242495903560731

Offset: 0

Peter Luschny, Jul 21 2020

sign

Cf. A033469 (denominators), A001896 (evaluated at x=+1/2).

a := n -> numer(`if`(n=0, 1, -2*n*Zeta(0, 1-2*n, -1/2))): seq(a(n), n=0..18);

a[0] := 1; a[n_] := -2 n HurwitzZeta[1 - 2 n, -1/2]; Array[a, 18, 0] // Numerator

a(n) = numerator(subst(bernpol(2*n, x), x, -1/2)); \\ Michel Marcus, Jul 21 2020

a(n) = Numerator(Bernoulli(2*n, -1/2)).

cp's OEIS Frontend

A001896 Numerators of cosecant numbers -2*(2^(2*n - 1) - 1)*Bernoulli(2*n); also of Bernoulli(2*n, 1/2) and Bernoulli(2*n, 1/4).

Views

Author

Keywords

Comments

Examples

References

Links

Crossrefs

Programs

Maple

Mathematica

PARI

Sage

Formula

A001897 Denominators of cosecant numbers: -2*(2^(2*n-1)-1)*Bernoulli(2*n).

Views

Author

Keywords

Comments

Examples

References

Links

Crossrefs

Programs

Magma

Maple

Mathematica

PARI

Sage

Formula

A157780 Denominator of Bernoulli(n, 1/2).

Views

Author

Keywords

Comments

Links

Crossrefs

Programs

Mathematica

Formula

A335948 T(n, k) = denominator([x^k] b_n(x)), where b_n(x) = Sum_{k=0..n} binomial(n,k)* Bernoulli(k, 1/2)*x^(n-k). Triangle read by rows, for n >= 0 and 0 <= k <= n.

Views

Author

Keywords

Comments

Examples

Crossrefs

A335954 a(n) = Numerator(-2*n*HurwitzZeta(1 - 2*n, -1/2)) for n > 0, and a(0) = 1.

Views

Author

Keywords

Crossrefs

Programs

Maple

Mathematica

PARI

Formula

A212655 Denominator of Bernoulli(2*n,1/2) / Period of length 2: repeat 12, 60.

Views

Author

Keywords

Comments

Examples

Crossrefs

Formula

A001896 Numerators of cosecant numbers -2(2^(2n - 1) - 1)Bernoulli(2n); also of Bernoulli(2n, 1/2) and Bernoulli(2n, 1/4).

A001897 Denominators of cosecant numbers: -2(2^(2n-1)-1)Bernoulli(2n).

A335954 a(n) = Numerator(-2nHurwitzZeta(1 - 2*n, -1/2)) for n > 0, and a(0) = 1.