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 1-9 of 9 results.

A126156 Expansion of e.g.f. sqrt(sec(sqrt(2)*x)), showing coefficients of only the even powers of x.

Original entry on oeis.org

1, 1, 7, 139, 5473, 357721, 34988647, 4784061619, 871335013633, 203906055033841, 59618325600871687, 21297483077038703899, 9127322584507530151393, 4621897483978366951337161, 2730069675607609356178641127, 1860452328661957054823447670979, 1448802510679254790311316267306753
Offset: 0

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Author

Paul D. Hanna, Dec 20 2006

Keywords

Comments

Previous name was: Column 0 and row sums of symmetric triangle A126155.
This is the square root of the Euler numbers (A122045) with respect to the Cauchy type product as described by J. Singh (see link and the second Maple program) normalized by 2^n. A241885 shows the corresponding sqrt of the Bernoulli numbers. - Peter Luschny, May 07 2014

Examples

			E.g.f.: A(x) = 1 + x^2/2! + 7*x^4/4! + 139*x^6/6! + 5473*x^8/8! + 357721*x^10/10! + ...
where the logarithm begins:
log(A(x)) = x^2/2! + 4*x^4/4! + 64*x^6/6! + 2176*x^8/8! + 126976*x^10/10! + 11321344*x^12/12! + ...
compare the logarithm to
A(x)^4 = 1 + 4*x^2/2! + 64*x^4/4! + 2176*x^6/6! + 126976*x^8/8! + 11321344*x^10/10! + ...
		

References

  • H. S. Wall, Analytic Theory of Continued Fractions, Chelsea 1973, p. 366.

Crossrefs

Diagonals: A126157, A126158.

Programs

  • Maple
    A126156 := proc(n)
            sqrt(sec(sqrt(2)*z)) ;
            coeftayl(%,z=0,2*n) ;
            %*(2*n)! ;
    end;
    seq(A126156(n),n=0..10) ; # Sergei N. Gladkovskii, Oct 31 2011
    g := proc(f, n) option remember; local g0, m; g0 := sqrt(f(0));
    if n=0 then g0 else if n=1 then 0 else add(binomial(n, m)*g(f,m)* g(f,n-m), m=1..n-1) fi; (f(n)-%)/(2*g0) fi end:
    a := n -> (-2)^n*g(euler, 2*n);
    seq(a(n), n=0..14); # Peter Luschny, May 07 2014
    # Alternative: an algorithm as described by Peter Bala, see also A365672:
    T := proc(n, k) option remember; if k = 0 then 1 else if k = n then
    T(n, k-1) else (n - k + 1) * (2 * (n - k) + 1) * T(n, k - 1) + T(n - 1, k)
    fi fi end:
    a := n -> T(n, n): seq(a(n), n = 0..14);  # Peter Luschny, Sep 29 2023
  • Mathematica
    a[n_] := SeriesCoefficient[ Sqrt[ Sec[ Sqrt[2]*x]], {x, 0, 2 n}]*(2*n)!; Table[a[n], {n, 0, 14}] (* Jean-François Alcover, Nov 29 2013, after Sergei N. Gladkovskii *)
  • Maxima
    a(n):=if n=0 then 1 else 1/(4*n)*sum(binomial(2*n,2*k)*((2^(2*k)-1)*2^(3*k)*(-1)^((k-1))*bern(2*k)*a(n-k)),k,1,n); /* Vladimir Kruchinin, Feb 25 2015 */
    
  • Maxima
    a[n]:=if n=0 then 1 else sum(a[n-k]*binomial(2*n,2*k)*(k/(2*n)-1)*(-2)^k,k,1,n);
    makelist(a[n],n,0,30); /* Tani Akinari, Sep 11 2023 */
    
  • PARI
    /* E.g.f. A(x) = exp( Integral^2 A(x)^4 dx^2 ): */
    {a(n)=local(A=1+x*O(x)); for(i=1, n, A=exp(intformal(intformal(A^4 + x*O(x^(2*n))))) ); (2*n)!*polcoeff(A, 2*n, x)}
    for(n=0,20,print1(a(n),", "))
    
  • PARI
    {a(n) = local(A=1+x); for(i=1,n, A = exp( intformal( A^2 * intformal( 1/A^2 + x*O(x^n)) ) ) ); n!*polcoeff(A,n)}
    for(n=0,20,print1(a(2*n),", "))
    
  • PARI
    {a(n)=-(n<1)-sum(j=0,n,sum(k=0,j/2,(2*n+1)!*(2*k-j)^(2*n)/(n!*(2*j+1)*(n-j)!*k!*(j-k)!*(-2)^(n+j-1))))}; /* Tani Akinari, Sep 28 2023 */
    
  • SageMath
    def A126156(n): return A126155(n, 0)
    print([A126156(n) for n in range(17)])  # Peter Luschny, Dec 14 2023

Formula

a(n) = Sum_{k=0..n} A087736(n,k)*3^(n-k). - Philippe Deléham, Jul 17 2007
E.g.f.: Sum_{n>=0} a(n)*x^(2*n)/(2*n)! = sqrt(sec(sqrt(2)*x)). - David Callan, Jan 03 2011
E.g.f. satisfies: A(x) = exp( Integral Integral A(x)^4 dx dx ), where A(x) = Sum_{n>=0} a(n)*x^(2*n)/(2*n)! and the constant of integration is zero. - Paul D. Hanna, May 30 2015
E.g.f. satisfies: A(x) = exp( Integral A(x)^2 * Integral 1/A(x)^2 dx dx ), where A(x) = Sum_{n>=0} a(n)*x^(2*n)/(2*n)! and the constant of integration is zero. - Paul D. Hanna, Jun 02 2015
G.f.: 1/(1-x/(1-6*x/(1-15*x/(1-28*x/(1-45*x/(1-66*x/(1-91*x/(1-... or 1/U(0) where U(k) = 1-x*(k+1)*(2*k+1)/U(k+1); (continued fraction). [See Wall.] - Sergei N. Gladkovskii, Oct 31 2011
G.f.: 1/U(0) where U(k) = 1 - (4*k+1)*(4*k+2)*x/(2 - (4*k+3)*(4*k+4)*x/ U(k+1)); (continued fraction, 2-step). - Sergei N. Gladkovskii, Oct 24 2012
G.f.: 1/G(0) where G(k) = 1 -x*(k+1)*(2*k+1)/G(k+1); (continued fraction). - Sergei N. Gladkovskii, Jan 11 2013
G.f.: Q(0), where Q(k) = 1 - x*(2*k+1)*(k+1)/( x*(2*k+1)*(k+1) - 1/Q(k+1)); (continued fraction). - Sergei N. Gladkovskii, Oct 09 2013
a(n) ~ 2^(5*n+2) * n^(2*n) / (exp(2*n) * Pi^(2*n+1/2)). - Vaclav Kotesovec, Jul 13 2014
a(n) = (1/(4*n))*Sum_{k=1..n} binomial(2*n,2*k)*((2^(2*k)-1)*2^(3*k)*(-1)^((k-1))*Bernoulli(2*k)*a(n-k)), a(0)=1. - Vladimir Kruchinin, Feb 25 2015
a(n) = Sum_{k=1..n} a(n-k)*binomial(2*n,2*k)*(k/(2*n)-1)*(-2)^k, a(0)=1. - Tani Akinari, Sep 11 2023
For n > 0, a(n) = -Sum_{j=0..n} Sum_{k=0..floor(j/2)} (2*n+1)!*(2*k-j)^(2*n)/(n!*(2*j+1)*(n-j)!*k!*(j-k)!*(-2)^(n+j-1)). - Tani Akinari, Sep 28 2023

Extensions

New name based on a comment of David Callan, Peter Luschny, May 07 2014

A222411 Numerators in Taylor series expansion of (x/(exp(x) - 1))^(3/2)*exp(x/2).

Original entry on oeis.org

1, -1, -1, 5, 7, -19, -869, 715, 2339, -200821, -12863, 2117, 7106149, -64604977, -131301607, 7629931291, 174053933, -19449462373, -46949081169401, 355455588729389, 10635113572583999, -6511303438681407901, -349640201588122693, 9112944418860287
Offset: 0

Views

Author

N. J. A. Sloane, Feb 28 2013

Keywords

Examples

			The first few fractions are 1, -1/4, -1/32, 5/384, 7/10240, -19/40960, -869/61931520, 715/49545216, ... = A222411/A222412. - _Petros Hadjicostas_, May 14 2020
		

Crossrefs

Cf. A222412 (denominators).

Programs

  • Maple
    gf:= (x/(exp(x)-1))^(3/2)*exp(x/2):
    a:= n-> numer(coeff(series(gf, x, n+3), x, n)):
    seq(a(n), n=0..25);  # Alois P. Heinz, Mar 02 2013
  • Mathematica
    Series[(x/(Exp[x]-1))^(3/2)*Exp[x/2], {x, 0, 25}] // CoefficientList[#, x]& // Numerator (* Jean-François Alcover, Mar 18 2014 *)

Formula

Theorem: A241885(n)/A242225(n) = n!*A222411(n)/(A222412(n)*(-1)^n/(1-2*n)) = n!*A350194(n)/(A350154(n)*(2*n+1)). - David Broadhurst, Apr 23 2022 (see Link).

A222412 Denominators in Taylor series expansion of (x/(exp(x) - 1))^(3/2)*exp(x/2).

Original entry on oeis.org

1, 4, 32, 384, 10240, 40960, 61931520, 49545216, 7927234560, 475634073600, 1993133260800, 177167400960, 48753634065776640, 195014536263106560, 39002907252621312000, 842462796656620339200, 2204424056667635712000, 79359266040034885632000
Offset: 0

Views

Author

N. J. A. Sloane, Feb 28 2013

Keywords

Examples

			The first few fractions are 1, -1/4, -1/32, 5/384, 7/10240, -19/40960, -869/61931520, 715/49545216, ... = A222411/A222412. - _Petros Hadjicostas_, May 14 2020
		

Crossrefs

Programs

  • Maple
    gf:= (x/(exp(x)-1))^(3/2)*exp(x/2):
    a:= n-> denom(coeff(series(gf, x, n+3), x, n)):
    seq(a(n), n=0..25);  # Alois P. Heinz, Mar 02 2013
  • Mathematica
    Series[(x/(Exp[x]-1))^(3/2)*Exp[x/2], {x, 0, 25}] // CoefficientList[#, x]& // Denominator (* Jean-François Alcover, Mar 18 2014 *)

Formula

Theorem: A241885(n)/A242225(n) = n!*A222411(n)/(A222412(n)*(-1)^n/(1-2*n)) = n!*A350194(n)/(A350154(n)*(2*n+1)). - David Broadhurst, Apr 23 2022 (see Link).

A242225 Write the coefficient of x^n/n! in the expansion of (x/(exp(x)-1))^(1/2) as f(n)/g(n); sequence gives g(n).

Original entry on oeis.org

1, 4, 48, 64, 1280, 3072, 86016, 49152, 2949120, 1310720, 11534336, 4194304, 1526726656, 2348810240, 12079595520, 3221225472, 73014444032, 51539607552, 137095356088320, 5772436045824, 3809807790243840, 725677674332160, 2023101395107840, 3166593487994880
Offset: 0

Views

Author

Jitender Singh, May 08 2014

Keywords

Comments

For f(n) see A241885(n).
The old definition was "Denominator of (B_n)^(1/2) in the Cauchy type product (sometimes known as binomial transform) where B_n is the n-th Bernoulli number".
The Nørlund polynomials N(a, n, x) with parameter a = 1/2 evaluated at x = 0 give the rational values. - Peter Luschny, Feb 18 2024

Examples

			For n=1, B_1=-1/2 and B_1^(1/2)=-1/4 so a(1)=4.
For n=6, B_6=1/6 and B_6^(1/2)=79/86016 so a(6)=86016.
		

Crossrefs

Programs

  • Maple
    g := proc(f, n) option remember; local g0, m; g0 := sqrt(f(0));
    if n=0 then g0 else if n=1 then 0 else add(binomial(n, m)*g(f, m)*g(f, n-m), m=1..n-1) fi; (f(n)-%)/(2*g0) fi end:
    a := n -> denom(g(bernoulli, n));
    seq(a(n), n=0..23);
  • Mathematica
    a := 1
    g[0] := Sqrt[f[0]]
    f[k_] := BernoulliB[k]
    g[1] := f[1]/(2 g[0]^1);
    g[k_] := (f[k] - Sum[Binomial[k, m] g[m] g[k - m], {m, 1, k - 1}])/(2 g[0])
    Table[Denominator[Factor[g[k]]], {k, 0, 15}] // TableForm
    (* Alternative: *)
    Table[Denominator@NorlundB[n, 1/2, 0], {n, 0, 23}] (* Peter Luschny, Feb 18 2024 *)

Formula

Theorem: A241885(n)/A242225(n) = n!*A222411(n)/(A222412(n)*(-1)^n/(1-2*n)) = n!*A350194(n)/(A350154(n)*(2*n+1)). - David Broadhurst, Apr 23 2022 (see Link).
For any arithmetic function f and a positive integer k>1, define the k-th root of f to be the arithmetic function g such that g*g*...*g(k times)=f and is determined by the following recursive formula:
g(0)= f(0)^{1/m};
g(1)= f(1)/(mg(0)^(m-1));
g(k)= 1/(m g(0)^{m-1})*(f(k)-sum_{k_1+...+k_m=k,k_i=2.
This formula is applicable for any rational root of an arithmetic function with respect to the Cauchy type product.

Extensions

Simpler definition from N. J. A. Sloane, Apr 24 2022 at the suggestion of David Broadhurst.

A350154 a(n) = denominator(k^n * [x^(2*n+1)] sqrt(k)*arccos(exp(-x^2/(2*k)))) for n >= 0 and fixed k > 0.

Original entry on oeis.org

1, 12, 480, 2688, 92160, 4055040, 805109760, 148635648, 2021444812800, 9037047398400, 41855798476800, 85571854663680, 1218840851644416000, 131634811977596928000, 30539276378802487296000, 26116346696355230515200, 72745993870031978496000, 8332722934203662991360000
Offset: 0

Views

Author

Robert B Fowler, Dec 16 2021

Keywords

Comments

Denominators of a power series characterizing how powers of the cosine function converge to the Gaussian function.
As the cosine function is raised to increasing powers k, it converges to the Gaussian normal function. Let x be the standard deviation argument of the Gaussian function, and define a suitably scaled cosine function.
G(x) = exp(-x^2/2), Gaussian function.
C(x,k) = (cos(x/sqrt(k)))^k, k-th power of cosine function
C(x,k) - G(x) = -x^4/(12k) + x^6/(24k) - x^6/(45x^2) + ...
The usefulness of this approximation lies within the "principal half-period" of C(x,k), defined as h_k = {x : abs(x) < sqrt(k)*Pi/2}. Within h_k, k can be any real number and C(x,k) is a good approximation to G(x) even for small k, although convergence to G(x) is only reciprocal in k. Outside h_k, negative cosine values occur and the approximation deteriorates.
If we define x(k) such that G(x) = C(x(k),k) then
x = lim_{k->infinity} x(k).
The value of x(k) can be expressed as a polynomial in integer powers of x and k and coefficients A350194(n)/a(n), and characterizes how closely cosine powers approximate and converge to the Gaussian function.

Examples

			x(k) = x - (1/12)*(x^3/k) + (1/480)*(x^5/k^2) + (1/2688)*(x^7/k^3) - (1/92160)*(x^9/k^4) - (19/4055040)*(x^11/k^5) + (79/805109760)*(x^13/k^6) ...
		

Crossrefs

Programs

  • Maple
    gf := sqrt(k)*arccos(exp(-x^2/(2*k))): assume(k > 0): assume(x > 0):
    ser := series(gf, x, 80): seq(denom(k^n*coeff(ser, x, 2*n+1)), n=0..17); # Peter Luschny, Dec 19 2021

Formula

The definitions of G(x) and C(x,k) lead directly to the equation
x(k) = sqrt(k)*arccos(exp(-x^2/(2k))),
which can be expanded into the power series
x(k) = Sum_{n>=0} (x^(2n+1)/k^n) * (A350194(n)/a(n)).
Theorem: A241885(n)/A242225(n) = n!*A222411(n)/(A222412(n)*(-1)^n/(1-2*n)) = n!*A350194(n)/(A350154(n)*(2*n+1)). - David Broadhurst, Apr 23 2022 (see Link).

A350194 Numerators of a power series characterizing how powers of the cosine function converge to the Gaussian function.

Original entry on oeis.org

1, -1, 1, 1, -1, -19, 79, 11, -2339, -11813, 677, 2117, -308963, -64604977, 131301607, 263101079, -5614643, -1768132943, 46949081169401, 9606907803497, -10635113572583999, -158812278992229461, 8131167478793551, 9112944418860287, -40395223967437706149
Offset: 0

Views

Author

Robert B Fowler, Dec 19 2021

Keywords

Comments

See A350154 for the denominators of this sequence of rational coefficients, as well as relevant comments, formulae, and examples.

Crossrefs

Cf. A350154.

Formula

Theorem: A241885(n)/A242225(n) = n!*A222411(n)/(A222412(n)*(-1)^n/(1-2*n)) = n!*A350194(n)/(A350154(n)*(2*n+1)). - David Broadhurst, Apr 23 2022 (see Link).

A370414 T(n, k) = numerator([x^n] N(1/2, n, x)) where N(a, n, x) is the n-th Nørlund polynomial.

Original entry on oeis.org

1, -1, 1, 1, -1, 1, 1, 1, -3, 1, -3, 1, 1, -1, 1, -19, -3, 5, 5, -5, 1, 79, -19, -9, 5, 5, -3, 1, 275, 79, -133, -21, 35, 7, -7, 1, -2339, 275, 79, -133, -21, 7, 7, -2, 1, -11813, -2339, 825, 79, -399, -189, 21, 3, -9, 1, 14217, -11813, -2339, 1375, 395, -399, -63, 15, 15, -5, 1
Offset: 0

Views

Author

Peter Luschny, Feb 18 2024

Keywords

Comments

Nørlund polynomials N(a, n, x) are generalizations of the powers 1, x, x^2, ... as well as of the Bernoulli polynomials 1, x - 1/2, x^2 - x + 1/6, ...
Parameter a = 0 gives the first case and a = 1 the second case. Here, we consider the case a = 1/2. You can think of it as a kind of square root of the Bernoulli polynomials. We give the coefficients of these polynomials, this sequence for the numerators, and A370415 for the denominators.
We also give the values of these polynomials at the point x = 1, which are analogous to the Bernoulli numbers; A370416 for the numerators, and A370417 for the denominators.

Examples

			The lists of rational coefficients start:
  [0] [        1]
  [1] [     -1/4,        1]
  [2] [     1/48,     -1/2,         1]
  [3] [     1/64,     1/16,      -3/4,       1]
  [4] [  -3/1280,     1/16,       1/8,      -1,     1]
  [5] [ -19/3072,   -3/256,      5/32,    5/24,  -5/4,    1]
  [6] [ 79/86016,  -19/512,    -9/256,    5/16,  5/16, -3/2,    1]
  [7] [275/49152, 79/12288, -133/1024, -21/256, 35/64, 7/16, -7/4, 1]
		

Crossrefs

Programs

  • Maple
    egf := (t/(exp(t) - 1))^(1/2)*exp(z*t):
    ser := series(egf, t, 16): ct := n -> n!*coeff(ser, t, n):
    seq(seq(numer(coeff(ct(n), z, k)), k = 0..n), n = 0..10);
  • Mathematica
    Table[Numerator@CoefficientList[NorlundB[n, 1/2, x], x] , {n, 0, 10}] // Flatten

Formula

T(n, k) = numerator( n! * [z^k] [t^n] (t / (exp(t) - 1))^(1/2)*exp(z*t) ).

A242233 2^n*(C_n)^(1/2) in the Cauchy type product where C_n is the n-th Catalan number.

Original entry on oeis.org

1, 1, 3, 11, 41, 137, 347, 611, 5777, 98321, 677363, -4192197, -134908871, -617972327, 22749265099, 449951818387, -632325203423, -163681108703199, -2324079456844573, 33233931805782635, 1734259111955765577, 14135975420529458857, -777499293367428199109
Offset: 0

Views

Author

Peter Luschny, May 08 2014

Keywords

Crossrefs

Programs

  • Maple
    f := sqrt(exp(2*x)*(BesselI(0,2*x)-BesselI(1,2*x)));
    seq(2^n*n!*coeff(series(f,x,n+1),x,n),n=0..22);
    # Second program with function g from A241885:
    catalan := n -> binomial(2*n,n)/(n+1);
    a := n -> 2^n*g(catalan, n); seq(a(n), n=0..22);
  • Mathematica
    g[n_] := g[n] = (CatalanNumber[n] - Sum[Binomial[n, m] g[m] g[n - m], {m, 1, n - 1}])/2;
    a[0] = 1; a[n_] := 2^n g[n];
    Table[a[n], {n, 0, 22}] (* Jean-François Alcover, Aug 02 2019, from 2nd Maple program *)
  • Maxima
    a[n]:=if n=0 then 1 else sum(a[n-k]*binomial(n, k)*(2*k)!*(3*k/(2*n)-1)*2^k/(k!*(k+1)!), k, 1, n); makelist(a[n],n,0,50); /* Tani Akinari, Nov 05 2024 */

Formula

a(n) = 2^n*n!*[x^n](sqrt(exp(2*x)*(BesselI(0,2*x)-BesselI(1,2*x)))), where [x^n](f(x)) the coefficient of x^n in f(x).
For n > 0, a(n) = Sum_{k=1..n} a(n-k)*binomial(n,k)*(2*k)!*(3*k/(2*n)-1)*2^k/(k!*(k+1)!). - Tani Akinari, Nov 05 2024

A365671 a(n) = denominator(4^n * n! * [x^n] sqrt(x / (e^x - 1))).

Original entry on oeis.org

1, 1, 3, 1, 5, 3, 21, 3, 45, 5, 11, 1, 91, 35, 45, 3, 17, 3, 1995, 21, 3465, 165, 115, 45, 2925, 819, 189, 7, 145, 5, 341, 11, 1309, 119, 1, 1, 9139, 247, 65, 7, 2255, 495, 148995, 3465, 108675, 2415, 1645, 7, 270725, 5525, 21879, 429, 583, 33, 4389, 399, 4959
Offset: 0

Views

Author

Peter Luschny, Sep 29 2023

Keywords

Crossrefs

Cf. A241885 (numerator), A126156.

Programs

  • Maple
    egf := sqrt(x/(exp(x)-1)): ser := series(egf, x, 64):
    seq(denom(4^n*n!*coeff(ser,x,n)), n = 0..56);
    # Alternative, using the Singh transformation 'g' from Maple in A126156:
    b := n -> 4^n*g(bernoulli, n); seq(denom(b(n)), n = 0..56);
Showing 1-9 of 9 results.