cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-10 of 11 results. Next

A050970 Numerator of S(n)/Pi^n, where S(n) = Sum_{k=-inf..+inf} (4k+1)^(-n).

Original entry on oeis.org

1, 1, 1, 1, 5, 1, 61, 17, 277, 31, 50521, 691, 540553, 5461, 199360981, 929569, 3878302429, 3202291, 2404879675441, 221930581, 14814847529501, 4722116521, 69348874393137901, 56963745931, 238685140977801337, 14717667114151
Offset: 1

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Author

Keywords

Comments

Reduced numerators of Favard constants.

Examples

			The first few values of S(n)/Pi^n are 1/4, 1/8, 1/32, 1/96, 5/1536, 1/960, ...
		

Crossrefs

Denominators: A068205. See also A050971.

Programs

  • Maple
    S := proc(n, k) option remember; if k = 0 then `if`(n = 0, 1, 0) else
    S(n, k - 1) + S(n - 1, n - k) fi end: EZ := n -> S(n, n)/(2^n * n!):
    A050970 := n -> numer(EZ(n-1)): seq(A050970(n), n=1..26); # Peter Luschny, Aug 02 2017
    # alternative
    A050970 := proc(n)
        if type(n,'even') then
            (-1)^(n/2)*2^(n-2)/(n-1)!*euler(n-1,0) ;
        else
            (-1)^((n-1)/2)*2^(n-2)/(n-1)!*euler(n-1,1/2) ;
        end if;
        %/2^n ;
        numer(%) ;
    end proc:
    seq(A050970(n),n=1..20) ; # R. J. Mathar, Jun 26 2024
  • Mathematica
    s[n_] := Sum[(4*k + 1)^(-n), {k, -Infinity, Infinity}]; a[n_] := Numerator[FullSimplify[s[n]/Pi^n]]; a[1] = 1; Table[a[n], {n, 1, 26}] (* Jean-François Alcover, Oct 25 2012 *)
    s[n_?EvenQ] := (-1)^(n/2-1)*(2^n-1)*BernoulliB[n]/(2*n!); s[n_?OddQ] := (-1)^((n-1)/2)*2^(-n-1)*EulerE[n-1]/(n-1)!; Table[s[n] // Numerator, {n, 1, 26}] (* Jean-François Alcover, May 13 2013 *)
    a[n_] := 4*Sum[((-1)^k/(2*k+1))^n, {k, 0, Infinity}] /. Pi -> 1 // Numerator; Table[a[n], {n, 1, 26}] (* Jean-François Alcover, Jun 20 2014 *)
    Table[4/(2 Pi)^n LerchPhi[(-1)^n, n, 1/2], {n, 21}] // Numerator (* Eric W. Weisstein, Aug 02 2017 *)
    Table[4/Pi^n If[Mod[n, 2] == 0, DirichletLambda, DirichletBeta][n], {n, 21}] // Numerator (* Eric W. Weisstein, Aug 02 2017 *)
  • PARI
    {a(n) = if( n<0, 0, numerator( polcoeff( 1 / (1 - tan(x/4 + x * O(x^n))), n)))}; /* Michael Somos, Nov 11 2014 */

Formula

There is a simple formula in terms of Euler and Bernoulli numbers.
a(2n) = A046976(n), a(2n+1) = A089171(n+1) (conjectured).
Numerator of coefficients of expansion of (sec(x/2) + tan(x/2) + 1)/2 in powers of x. - Sergei N. Gladkovskii, Nov 11 2014

Extensions

Entry revised by N. J. A. Sloane, Mar 24 2002

A245198 Decimal expansion of the Landau-Kolmogorov constant C(3,1) for derivatives in the case L_infinity(-infinity, infinity).

Original entry on oeis.org

1, 0, 4, 0, 0, 4, 1, 9, 1, 1, 5, 2, 5, 9, 5, 2, 0, 5, 7, 2, 6, 5, 0, 2, 8, 4, 1, 2, 1, 7, 8, 9, 4, 2, 6, 9, 3, 1, 6, 8, 9, 0, 2, 6, 7, 0, 1, 8, 6, 6, 3, 1, 0, 5, 4, 8, 4, 8, 7, 9, 5, 5, 4, 0, 1, 0, 0, 0, 5, 3, 1, 5, 5, 6, 9, 8, 6, 3, 4, 3, 8, 6, 8, 0, 3, 0, 2, 8, 3, 1, 8, 3, 9, 5, 3, 7, 8, 7, 4, 3, 3, 6, 4, 3
Offset: 1

Views

Author

Jean-François Alcover, Jul 17 2014

Keywords

Comments

The corresponding Landau-Kolmogorov inequality for the first and third derivative is ||f'|| <= C(3,1) ||f||^(2/3) ||f'''||^(1/3) [see S. Finch ref. for C(n,k) and the general derivative inequalities], where the real-valued function f is defined on (-infinity, infinity), the involved norm being the supremum norm, defined by ||f|| = sup |f(x)|.
Hadamard proved that if f is twice differentiable and both f and f'' are bounded, then ||f'|| <= sqrt(2) ||f||^(1/2) ||f''||^(1/2), and the constant C(2,1) = sqrt(2) is the best possible.
Kolmogorov determined best constants C(n,k), 1 <= k <= n, for the inequality between derivatives in terms of Favard constants (A050970/A050971). These formulas giving C(n,k) include special cases discovered by G. E. Shilov for small values of n and k.
[All comments made after Steven R. Finch].

Examples

			1.0400419115259520572650284121789426931689026701866310548487955401...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 3.3 Landau-Kolmogorov constants, p. 213.

Crossrefs

Programs

  • Mathematica
    a[n_] := (4/Pi)*Sum[((-1)^j/(2*j+1))^(n+1), {j, 0, Infinity}]; c[n_, k_] := a[n-k]*a[n]^(-1+k/n); RealDigits[c[3, 1], 10, 104] // First
    (* or, directly: *) RealDigits[3^(2/3)/2, 10, 104] // First

Formula

C(n,k) = a(n-k)*a(n)^(-1+k/n), where a(n) = (4/Pi)*sum_{j=0..infinity}((-1)^j/(2j+1))^(n+1) or a(n) = 4*Pi^n*f(n+1), f(n) being the n-th Favard constant A050970(n)/A050971(n).
C(3,1) = 3^(2/3)/2 = (9/8)^(1/3).

A246006 a(2n) = numerator of |Bernoulli(2n)|, a(2n+1) = Euler(2n).

Original entry on oeis.org

1, 1, 1, 1, 1, 5, 1, 61, 1, 1385, 5, 50521, 691, 2702765, 7, 199360981, 3617, 19391512145, 43867, 2404879675441, 174611, 370371188237525, 854513, 69348874393137901, 236364091, 15514534163557086905, 8553103, 4087072509293123892361, 23749461029, 1252259641403629865468285
Offset: 0

Views

Author

Eric Chen, Nov 13 2014

Keywords

Comments

Primes p which divide at least one a(n) for n<=p-2 are called weakly-irregular primes. For example, 19|a(11), 31|a(23), 37|a(32), 43|a(13), 47|a(15), 59|a(44), 61|a(7), ... - Eric Chen, Nov 26 2014
The weakly-irregular primes below 500 are 19, 31, 37, 43, 47, 59, 61, 67, 71, 79, 101, 103, 131, 137, 139, 149, 157, 193, 223, 233, 241, 251, 257, 263, 271, 277, 283, 293, 307, 311, 347, 349, 353, 359, 373, 379, 389, 401, 409, 419, 421, 433, 461, 463, 467, 491. - Eric Chen, Nov 26 2014
A prime can divide more than one a(n) for n<=p-2; for example, 67 divides both a(27) and a(58); additional examples are 101, 149, 157, 241, 263, 307, 311, ... . - Eric Chen, Nov 26 2014
Smallest values of k such that the n-th weakly-irregular prime divides a(k) are 11, 23, 32, 13, 15, 44, 7, 27, 29, 19, 63, 24, 22, 43, 129, 130, 62, 75, ... . - Eric Chen, Nov 26 2014
Smallest prime factors (>= n+2) of a(n) are 1, 1, 1, 1, 1, 1, 1, 61, 1, 277, 1, 19, 691, 43, 1, 47, 3617, 228135437, 43867, 79, 283, 41737, 131, 31, 103, 2137, 657931, 67, 9349, 71, ... . - Eric Chen, Nov 26 2014
The irregular pairs are (61, 7), (277, 9), (19, 11), (2659, 11), (691, 12), (43, 13), (967, 13), (47, 15), (4241723, 15), (3617, 16), (228135437, 17), (43867, 18), (79, 19), (349, 19), (84224971, 19), ... . - Eric Chen, Nov 26 2014

Examples

			Euler(10) = 50521, so a(11) = 50521.
Bernoulli(12) = 691/2730, so a(12) = 691.
		

Crossrefs

Programs

  • Mathematica
    a246006[n_] := If[EvenQ[n], Abs[Numerator[BernoulliB[n]]], Abs[EulerE[n-1]]]; Table[a246006[n], {n, 0, 99}]
  • Python
    from sympy import euler, bernoulli
    def A246006(n): return abs(euler(n-1)) if n&1 else abs(bernoulli(n)).p # Chai Wah Wu, Apr 15 2023

A245294 Decimal expansion of the square root of 6/5.

Original entry on oeis.org

1, 0, 9, 5, 4, 4, 5, 1, 1, 5, 0, 1, 0, 3, 3, 2, 2, 2, 6, 9, 1, 3, 9, 3, 9, 5, 6, 5, 6, 0, 1, 6, 0, 4, 2, 6, 7, 9, 0, 5, 4, 8, 9, 3, 8, 9, 9, 9, 5, 9, 6, 6, 5, 0, 8, 4, 5, 3, 7, 8, 8, 8, 9, 9, 4, 6, 4, 9, 8, 6, 5, 5, 4, 2, 4, 5, 4, 4, 5, 4, 6, 7, 6, 0, 1, 7, 1, 6, 8, 7, 2, 3, 2, 7, 7, 4, 1, 2, 5, 1, 5, 2, 9, 4, 5
Offset: 1

Views

Author

Jean-François Alcover, Jul 17 2014

Keywords

Comments

Decimal expansion of the Landau-Kolmogorov constant C(4,2) for derivatives in the case L_infinity(infinity, infinity).
See A245198.
Apart from the first digit the same as A176057. - R. J. Mathar, Jul 21 2014

Examples

			1.095445115010332226913939565601604267905489389995966508453788899464986554...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 3.3 Landau-Kolmogorov constants, p. 213.

Crossrefs

Programs

  • Mathematica
    a[n_] := (4/Pi)*Sum[((-1)^j/(2*j+1))^(n+1), {j, 0, Infinity}]; c[n_, k_] := a[n-k]*a[n]^(-1+k/n); RealDigits[c[4, 2], 10, 105] // First
    RealDigits[Sqrt[6/5], 10, 100][[1]] (* Amiram Eldar, Jul 19 2022 *)
  • PARI
    sqrt(6/5) \\ Charles R Greathouse IV, Aug 26 2017

Formula

C(n,k) = a(n-k)*a(n)^(-1+k/n), where a(n) = (4/Pi)*sum_{j=0..infinity}((-1)^j/(2j+1))^(n+1) or a(n) = 4*Pi^n*f(n+1), f(n) being the n-th Favard constant A050970(n)/A050971(n).
C(4,2) = sqrt(6/5).
Equals Sum_{k>=0} binomial(2*k,k)/24^k. - Amiram Eldar, Jul 19 2022

A162445 A sequence related to the Beta function.

Original entry on oeis.org

1, 8, 384, 46080, 2064384, 3715891200, 392398110720, 1428329123020800, 274239191619993600, 1678343852714360832000, 102043306245033138585600, 4714400748520531002654720000, 160144566965128191597871104000
Offset: 0

Views

Author

Johannes W. Meijer, Jul 06 2009

Keywords

Comments

We define F(z) = Beta(1/2-z/2,1/2+z/2)/Beta(1/2,1/2) = 1/sin(Pi*(1+z)/2) with Beta(z,w) the Beta function. See A008956 for a closely related function.
For the Taylor series expansion of F(z) we can write F(z) = sum(b(n)*(Pi*z)^(2*n)/a(n), n=0..infinity) with b(n) = A046976(n) and a(n) the sequence given above.
We can also write F(z) = sum(c(n)*(Pi*z)^(2*n)/d(n), n=0..infinity) with c(n) = A000364(n) and d(n) = A067624(n).
If p(n) is the exponent of the prime factor 2 in a(n) than p(n) = A120738(n) and 2^p(n) = A061549(n) = abs((4*n)!!/A117972(n)).

Crossrefs

Bisection of A050971
Equals 2^(2*n)*A046977(n)

Programs

  • Mathematica
    Denominator[Table[EulerE[2n]/(4n)!!,{n,0,20}]] (* Harvey P. Dale, Jun 23 2013 *)

Formula

a(n) = denom(euler(2*n)/(4*n)!!)

A245293 Decimal expansion of the Landau-Kolmogorov constant C(4,1) for derivatives in the case L_infinity(infinity, infinity).

Original entry on oeis.org

1, 0, 8, 0, 9, 6, 0, 1, 2, 3, 8, 4, 5, 6, 2, 7, 5, 1, 5, 1, 8, 8, 0, 8, 0, 1, 5, 0, 6, 3, 6, 5, 4, 5, 6, 4, 9, 2, 3, 7, 5, 7, 7, 0, 7, 4, 7, 2, 5, 5, 2, 3, 4, 3, 8, 0, 1, 3, 5, 6, 6, 4, 4, 2, 5, 9, 2, 7, 5, 9, 9, 0, 9, 7, 9, 0, 6, 6, 8, 5, 7, 2, 5, 0, 6, 8, 4, 8, 1, 8, 1, 1, 2, 7, 0, 7, 0, 7, 6, 1, 6, 1, 7, 7, 9
Offset: 1

Views

Author

Jean-François Alcover, Jul 17 2014

Keywords

Comments

See A245198.

Examples

			1.0809601238456275151880801506365456492375770747255234380135664425927599...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 3.3 Landau-Kolmogorov constants, p. 213.

Crossrefs

Programs

  • Mathematica
    a[n_] := (4/Pi)*Sum[((-1)^j/(2*j+1))^(n+1), {j, 0, Infinity}]; c[n_, k_] := a[n-k]*a[n]^(-1+k/n); RealDigits[c[4, 1], 10, 105] // First

Formula

C(n,k) = a(n-k)*a(n)^(-1+k/n), where a(n) = (4/Pi)*sum_{j=0..infinity}((-1)^j/(2j+1))^(n+1) or a(n) = 4*Pi^n*f(n+1), f(n) being the n-th Favard constant A050970(n)/A050971(n).
C(4,1) = 4*(2/3)^(1/4)/5^(3/4) = (512/375)^(1/4).

A245295 Decimal expansion of the Landau-Kolmogorov constant C(4,3) for derivatives in the case L_infinity(infinity, infinity).

Original entry on oeis.org

1, 4, 8, 0, 1, 6, 5, 6, 0, 8, 9, 8, 4, 5, 7, 0, 5, 0, 1, 1, 3, 3, 5, 7, 9, 9, 3, 2, 3, 2, 7, 6, 7, 3, 6, 3, 8, 5, 9, 8, 1, 2, 3, 5, 8, 2, 6, 1, 2, 3, 7, 6, 2, 3, 6, 6, 4, 9, 7, 2, 4, 8, 1, 1, 8, 3, 1, 4, 9, 3, 3, 7, 3, 1, 5, 9, 9, 2, 3, 0, 5, 2, 4, 0, 8, 8, 8, 3, 9, 0, 3, 8, 0, 3, 7, 6, 7, 9, 7, 3, 4, 5, 1, 4, 9
Offset: 1

Views

Author

Jean-François Alcover, Jul 17 2014

Keywords

Comments

See A245198.

Examples

			1.480165608984570501133579932327673638598123582612376236649724811831493373...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 3.3 Landau-Kolmogorov constants, p. 213.

Crossrefs

Programs

  • Mathematica
    a[n_] := (4/Pi)*Sum[((-1)^j/(2*j+1))^(n+1), {j, 0, Infinity}]; c[n_, k_] := a[n-k]*a[n]^(-1+k/n); RealDigits[c[4, 3], 10, 105] // First

Formula

C(n,k) = a(n-k)*a(n)^(-1+k/n), where a(n) = (4/Pi)*sum_{j=0..infinity}((-1)^j/(2j+1))^(n+1) or a(n) = 4*Pi^n*f(n+1), f(n) being the n-th Favard constant A050970(n)/A050971(n).
C(4,3) = (3/5)^(1/4)*2^(3/4) = (24/5)^(1/4).

A245296 Decimal expansion of the Landau-Kolmogorov constant C(5,1) for derivatives in the case L_infinity(infinity, infinity).

Original entry on oeis.org

1, 0, 4, 4, 2, 5, 7, 9, 0, 9, 3, 0, 9, 7, 9, 5, 1, 4, 3, 4, 4, 5, 3, 6, 9, 6, 1, 7, 1, 5, 5, 7, 0, 2, 5, 8, 3, 0, 8, 0, 4, 2, 0, 8, 0, 4, 2, 0, 2, 5, 3, 7, 2, 0, 7, 7, 5, 7, 6, 1, 3, 4, 1, 5, 8, 0, 0, 2, 3, 2, 5, 8, 8, 8, 0, 0, 6, 2, 3, 5, 7, 8, 8, 7, 4, 4, 6, 0, 2, 0, 1, 1, 1, 9, 2, 2, 0, 2, 7, 8, 5, 4, 7, 2, 4
Offset: 1

Views

Author

Jean-François Alcover, Jul 17 2014

Keywords

Comments

See A245198.

Examples

			1.0442579093097951434453696171557025830804208042025372077576134158002325888...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 3.3 Landau-Kolmogorov constants, p. 213.

Crossrefs

Programs

  • Mathematica
    a[n_] := (4/Pi)*Sum[((-1)^j/(2*j+1))^(n+1), {j, 0, Infinity}]; c[n_, k_] := a[n-k]*a[n]^(-1+k/n); RealDigits[c[5,1], 10, 105] // First

Formula

C(n,k) = a(n-k)*a(n)^(-1+k/n), where a(n) = (4/Pi)*sum_{j=0..infinity}((-1)^j/(2j+1))^(n+1) or a(n) = 4*Pi^n*f(n+1), f(n) being the n-th Favard constant A050970(n)/A050971(n).
C(5,1) = (5*5^(4/5))/(8*2^(4/5)*3^(1/5)) = (1953125/1572864)^(1/5).

A245297 Decimal expansion of the Landau-Kolmogorov constant C(5,2) for derivatives in the case L_infinity(infinity, infinity).

Original entry on oeis.org

1, 1, 1, 6, 6, 4, 5, 9, 7, 1, 1, 0, 3, 8, 0, 9, 8, 8, 2, 6, 4, 5, 7, 1, 5, 4, 5, 1, 0, 7, 3, 1, 5, 3, 1, 7, 8, 9, 6, 6, 5, 1, 2, 0, 0, 6, 6, 9, 7, 4, 0, 4, 0, 1, 6, 4, 5, 6, 3, 4, 2, 1, 6, 0, 6, 0, 8, 1, 7, 9, 5, 2, 8, 6, 4, 8, 5, 2, 2, 2, 9, 6, 8, 4, 6, 4, 6, 0, 0, 2, 6, 2, 2, 4, 5, 4, 9, 9, 1, 2, 3
Offset: 1

Views

Author

Jean-François Alcover, Jul 17 2014

Keywords

Comments

See A245198.

Examples

			1.1166459711038098826457154510731531789665120066974040164563421606...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 3.3 Landau-Kolmogorov constants, p. 213.

Crossrefs

Programs

  • Mathematica
    a[n_] := (4/Pi)*Sum[((-1)^j/(2*j+1))^(n+1), {j, 0, Infinity}]; c[n_, k_] := a[n-k]*a[n]^(-1+k/n); RealDigits[c[5,2], 10, 101] // First

Formula

C(n,k) = a(n-k)*a(n)^(-1+k/n), where a(n) = (4/Pi)*sum_{j=0..infinity}((-1)^j/(2j+1))^(n+1) or a(n) = 4*Pi^n*f(n+1), f(n) being the n-th Favard constant A050970(n)/A050971(n).
C(5,2) = (5*5^(4/5))/(8*2^(4/5)*3^(1/5)) = (1953125/1572864)^(1/5).

A245298 Decimal expansion of the Landau-Kolmogorov constant C(5,3) for derivatives in the case L_infinity(infinity, infinity).

Original entry on oeis.org

1, 1, 1, 9, 4, 2, 3, 7, 3, 1, 7, 3, 5, 1, 0, 7, 6, 1, 1, 6, 2, 9, 7, 1, 1, 0, 8, 2, 0, 8, 1, 2, 6, 1, 0, 4, 1, 2, 4, 9, 9, 8, 5, 5, 6, 7, 0, 5, 8, 6, 0, 7, 0, 8, 6, 5, 2, 0, 9, 8, 2, 7, 9, 9, 1, 3, 1, 5, 4, 2, 2, 9, 2, 2, 9, 6, 9, 0, 4, 5, 1, 5, 2, 5, 2, 6, 2, 8, 6, 5, 9, 6, 1, 3, 0, 8, 5, 2, 2, 9, 2, 9, 5, 2
Offset: 1

Views

Author

Jean-François Alcover, Jul 17 2014

Keywords

Comments

See A245198.

Examples

			1.11942373173510761162971108208126104124998556705860708652098279913...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 3.3 Landau-Kolmogorov constants, p. 213.

Crossrefs

Programs

  • Mathematica
    a[n_] := (4/Pi)*Sum[((-1)^j/(2*j+1))^(n+1), {j, 0, Infinity}]; c[n_, k_] := a[n-k]*a[n]^(-1+k/n); RealDigits[c[5,3], 10, 104] // First

Formula

C(n,k) = a(n-k)*a(n)^(-1+k/n), where a(n) = (4/Pi)*sum_{j=0..infinity}((-1)^j/(2j+1))^(n+1) or a(n) = 4*Pi^n*f(n+1), f(n) being the n-th Favard constant A050970(n)/A050971(n).
C(5,3) = (1/2)*(15/2)^(2/5).
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