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.

Previous Showing 31-40 of 73 results. Next

A371529 Decimal expansion of Product_{k>=2} (1 + (-1)^k/Lucas(k)).

Original entry on oeis.org

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

Views

Author

Amiram Eldar, Mar 26 2024

Keywords

Examples

			1.07248271775513062588537881652660869304392049333099...
		

Crossrefs

Programs

  • Mathematica
    With[{eta = DedekindEta, tau0 = Log[GoldenRatio]*I/Pi}, RealDigits[(Surd[GoldenRatio, 4] / Sqrt[5]) * eta[2*tau0]^3 * eta[3*tau0] / (eta[tau0]^2 * eta[4*tau0]), 10, 120][[1]]]
  • PARI
    prodinf(k = 2, 1 + (-1)^k/(fibonacci(k-1) + fibonacci(k+1)))

Formula

Equals Product_{k>=2} (1 + (-1)^k/A000032(k)).
Equals A371525 / (2*sqrt(5)).
Equals (phi^(1/4) / sqrt(5)) * eta(2*tau_0)^3 * eta(3*tau_0) / (eta(tau_0)^2 * eta(4*tau_0)), where phi is the golden ratio (A001622), tau_0 = i*log(phi)/Pi, and i = sqrt(-1) (Duverney et al., 2022).

A371530 Decimal expansion of Product_{k>=1} (1 - (-1)^k/Lucas(k)).

Original entry on oeis.org

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

Views

Author

Amiram Eldar, Mar 26 2024

Keywords

Examples

			1.50218004433245676912076258176556998802715258088888...
		

Crossrefs

Programs

  • Mathematica
    With[{eta = DedekindEta, tau0 = Log[GoldenRatio]*I/Pi}, RealDigits[2 * Surd[GoldenRatio, 4] * eta[2*tau0]^2 * eta[6*tau0]/(eta[3*tau0] * eta[4*tau0]), 10, 120][[1]]]
  • PARI
    prodinf(k = 1, 1 - (-1)^k/(fibonacci(k-1) + fibonacci(k+1)))

Formula

Equals Product_{k>=2} (1 - (-1)^k/A000032(k)).
Equals (2*sqrt(5)) * A371526.
Equals 2 * phi^(1/4) * eta(2*tau_0)^2 * eta(6*tau_0) / (eta(3*tau_0) * eta(4*tau_0)), where phi is the golden ratio (A001622), tau_0 = i*log(phi)/Pi, and i = sqrt(-1) (Duverney et al., 2022).

A139347 Decimal expansion of negated tangent of the golden ratio. That is, the decimal expansion of -tan((1+sqrt(5))/2).

Original entry on oeis.org

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

Views

Author

Mohammad K. Azarian, Apr 15 2008

Keywords

Comments

By the Lindemann-Weierstrass theorem, this constant is transcendental. - Charles R Greathouse IV, May 13 2019

Examples

			-21.15380078249327464858628117032582559788124367464826...
		

Crossrefs

Programs

Formula

Equals tan(A001622).
From Amiram Eldar, Feb 07 2022: (Start)
Equals 1/A139348.
Equals A139345/A139346. (End)

Extensions

Offset corrected by Mohammad K. Azarian, Dec 13 2008
Sign added to definition by R. J. Mathar, Feb 05 2009

A139348 Decimal expansion of negated cotangent of the golden ratio. That is, the decimal expansion of -cot((1+sqrt(5))/2).

Original entry on oeis.org

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

Views

Author

Mohammad K. Azarian, Apr 15 2008

Keywords

Comments

By the Lindemann-Weierstrass theorem, this constant is transcendental. - Charles R Greathouse IV, May 13 2019

Examples

			0.04727282866479448118935650960621633420056105722556...
		

Crossrefs

Programs

Formula

Equals cot(A001622).
From Amiram Eldar, Feb 07 2022: (Start)
Equals 1/A139347.
Equals A139346/A139345. (End)

Extensions

Added sign in definition. Leading zero dropped by R. J. Mathar, Feb 05 2009

A202541 Decimal expansion of the number x satisfying e^(2x) - e^(-2x) = 1.

Original entry on oeis.org

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

Views

Author

Clark Kimberling, Dec 21 2011

Keywords

Comments

See A202537 for a guide to related sequences. The Mathematica program includes a graph.
Archimedes's-like scheme: set p(0) = 1/(2*sqrt(5)), q(0) = 1/4; p(n+1) = 2*p(n)*q(n)/(p(n)+q(n)) (arithmetic mean of reciprocals, i.e., 1/p(n+1) = (1/p(n) + 1/q(n))/2), q(n+1) = sqrt(p(n+1)*q(n)) (geometric mean, i.e., log(q(n+1)) = (log(p(n+1)) + log(q(n)))/2), for n >= 0. The error of p(n) and q(n) decreases by a factor of approximately 4 each iteration, i.e., approximately 2 bits are gained by each iteration. Set r(n) = (2*q(n) + p(n))/3, the error decreases by a factor of approximately 16 for each iteration, i.e., approximately 4 bits are gained by each iteration. For a similar scheme see also A244644. - A.H.M. Smeets, Jul 12 2018

Examples

			0.24060591252980172374887945671218421156759216719...
		

Crossrefs

Programs

  • Mathematica
    u = 2; v = 2;
    f[x_] := E^(u*x) - E^(-v*x); g[x_] := 1
    Plot[{f[x], g[x]}, {x, -2, 2}, {AxesOrigin -> {0, 0}}]
    r = x /. FindRoot[f[x] == g[x], {x, .2, .3}, WorkingPrecision -> 110]
    RealDigits[r]   (* A202541 *)
    RealDigits[ Log[ (1+Sqrt[5])/2 ] / 2, 10, 99] // First (* Jean-François Alcover, Feb 27 2013 *)
    RealDigits[ FindRoot[ Exp[2x] - Exp[-2x] == 1, {x, 1}, WorkingPrecision -> 128][[1, 2]], 10, 111][[1]] (* Robert G. Wilson v, Jul 23 2018 *)
  • PARI
    asinh(1/2)/2 \\ Michel Marcus, Jul 12 2018

Formula

Equals (1/2)*arcsinh(1/2) or (1/2)*log(phi), phi being the golden ratio. - A.H.M. Smeets, Jul 12 2018
Equals Sum_{k>=1} (-1)^(k+1) * arctanh(1/Fibonacci(3*k)^2) (Melham and Shannon, 1995). - Amiram Eldar, Oct 04 2021
Equals A002390/2. - Alois P. Heinz, Jul 14 2022
Equals arctanh(sqrt(5)-2). - Amiram Eldar, Feb 09 2024

A349850 Decimal expansion of Sum_{k>=1} H(k)*F(k)/2^k, where H(k) = A001008(k)/A002805(k) is the k-th harmonic number and F(k) = A000045(k) is the k-th Fibonacci number.

Original entry on oeis.org

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

Views

Author

Amiram Eldar, Dec 02 2021

Keywords

Examples

			3.96874800690391485217106364061998568869842436396224...
		

Crossrefs

Programs

  • Mathematica
    RealDigits[2*Log[2] + 12*Log[GoldenRatio]/Sqrt[5], 10, 100][[1]]

Formula

Equals log(4*phi^(12/sqrt(5))) = 2*log(2) + 12*log(phi)/sqrt(5), where phi is the golden ratio (A001622).

A385445 Decimal expansion of (-1 + 3*phi)*sqrt(3 - phi), with the golden section phi = A001622.

Original entry on oeis.org

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

Views

Author

Wolfdieter Lang, Jul 01 2025

Keywords

Comments

This constant c gives the real part of -2*11*Z = (c + d*i), where Z is the (finite) fixed point of a complex function w (of the loxodromic type) mapping iteratively the vertices of golden triangles, starting with vertices (D_1, D_2, D_3), circumscribed by the unit circle with center at the origin, and D_1 = i, D_2 = (s - phi*i)/2 and D_3 = (-s - phi*i)/2. This function is w(z) = a*z + b, with a = (-1 + phi) * exp(-(3*Pi/5)*i) = -((2 - phi) + s*i)/2 and b = (1 - phi)*i, where s = sqrt(3 - phi) = A182007 (the length of the base (D_2, D_3) of the first triangle, also called s_1).
The imaginary part of -2*11*Z is d = -7 + 10*phi = A385446.
If the fixed point Z = -(0.20594... + 0.41728...*i) is chosen as origin then the loxodromic map is W(z') = a*z' (where z' = z - Z and W(z') = w(z'+Z) - Z).
For details see the linked paper, eqs.(5a,b) for w(z), eq.(6) for Z and eq.(7) for W(z'). (In eq.(5b) the i is missing in the exponent.) The nesting of golden triangles as shown in Fig. 1 of the link leads to the fixed point Z.
The vertices of the nested golden triangles can be connected by a spiral built of circular sections with angle 108 degrees, centered at vertices D_{n+3} and shrinking radii s_n =(- 1 + phi)^(n-1)*s. Note that the curvature of this spiral is not continuous.
The length(Z, D_n) =: rho_n of the spokes of the spiral is (-1 + phi)^(n-1)*rho_1, with sqrt(11)*rho_1 = sqrt(8 + 9*phi) = sqrt(5 + 7*phi)*s = A385447.
For the length ratio rho_1/s see A385448.
The logarithmic spiral connecting the vertices D_{n+1} is given in polar coordinates by rho(Phi) = rho_1 * exp((-(5/(3*Pi)) * log(phi)*Phi), with the vertices obtained in polar coordinates for Phi = Phi_n = (3*Pi/5)*n, namely rho(Phi_n) = rho_{n+1}, for n >= 0. For log(phi) see A002390. Note that the nonnegative x-axis is now along Z, D_1. The angle(Z, D1, D4) =: gamma is given by arctan((18 - 11*phi)/s) = arcsin(rho_4 / 2) = 0.169860704... or 9.7323... degrees. See Fig. 3 of the linked paper.

Examples

			4.5307685931859751743612240909981473232388869294682093...
		

Crossrefs

Programs

  • Mathematica
    RealDigits[Sqrt[27 - 4*GoldenRatio], 10, 120][[1]] (* Amiram Eldar, Jul 02 2025 *)

Formula

Equals (-1 + 3*phi)*sqrt(3 - phi) = (A090550 - 2)*A182007.
Equals sqrt(27 - 4*phi).

A072876 a(1) = a(2) = a(3) = a(4) = 1 and a(n) = (a(n-1)*a(n-3) + a(n-2)^3)/a(n-4) for n >= 5.

Original entry on oeis.org

1, 1, 1, 1, 2, 3, 11, 49, 739, 41926, 36876163, 1504578225617, 67856786028033600651, 81238311359334144709516343054051, 8472940010945536421401513734595877223414710434640386
Offset: 1

Views

Author

Benoit Cloitre, Jul 28 2002

Keywords

Comments

A variation of a Somos-4 sequence with a(n-2)^3 in place of a(n-2)^2.

Crossrefs

Programs

  • Mathematica
    Nest[Append[#, (#[[-1]]*#[[-3]] + #[[-2]]^3)/#[[-4]] ] &, {1, 1, 1, 1}, 11] (* Michael De Vlieger, May 12 2019 *)
    RecurrenceTable[{a[1]==a[2]==a[3]==a[4]==1,a[n]==(a[n-1]a[n-3]+a[n-2]^3)/ a[n-4]},a,{n,20}] (* Harvey P. Dale, May 15 2019 *)

Formula

Lim_{n->infinity} (log(log a(n)))/n = log((1+sqrt(5))/2) or about 0.48. See A002390. However, convergence is extremely slow. - Andrew Hone, Nov 15 2005
From Jon E. Schoenfield, May 12 2019: (Start)
It appears that, for n >= 1,
a(n) = ceiling(e^(c0*phi^n + d0/phi^n)) if n is even,
ceiling(e^(c1*phi^n + d1/phi^n)) if n is odd,
where
phi = (1 + sqrt(5))/2,
c0 = 0.087172479898911051233710515749226588954735607680...
c1 = 0.087662681482404614007222542134598226046349621976...
d0 = -9.574280373370101810186207466479291633433387765559...
d1 = -4.425515288739040257644546086989175506652492968654...
(End)

A129187 Decimal expansion of arcsinh(1/3).

Original entry on oeis.org

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

Views

Author

N. J. A. Sloane, Jul 27 2008

Keywords

Comments

Archimedes's-like scheme: set p(0) = 1/sqrt(10), q(0) = 1/3; p(n+1) = 2*p(n)*q(n)/(p(n)+q(n)) (arithmetic mean of reciprocals, i.e., 1/p(n+1) = (1/p(n) + 1/q(n))/2), q(n+1) = sqrt(p(n+1)*q(n)) (geometric mean, i.e., log(q(n+1)) = (log(p(n+1)) + log(q(n)))/2), for n >= 0. The error of p(n) and q(n) decreases by a factor of approximately 4 each iteration, i.e., approximately 2 bits are gained by each iteration. Set r(n) = (2*q(n) + p(n))/3, the error decreases by a factor of approximately 16 for each iteration, i.e., approximately 4 bits are gained by each iteration. For a similar scheme see also A244644. - A.H.M. Smeets, Jul 12 2018

Examples

			0.32745015023725844332253525998825812770052452899076745127562...
		

Crossrefs

Programs

Formula

Equals log((1 + sqrt(10))/3). - Jianing Song, Jul 12 2018
Equals arccoth(sqrt(10)). - Amiram Eldar, Feb 09 2024

A139349 Decimal expansion of negated secant of the golden ratio. That is, the decimal expansion of -sec((1+sqrt(5))/2).

Original entry on oeis.org

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

Views

Author

Mohammad K. Azarian, Apr 15 2008

Keywords

Comments

By the Lindemann-Weierstrass theorem, this constant is transcendental. - Charles R Greathouse IV, May 13 2019

Examples

			21.17742400636614440872804040937130213307185355364174...
		

Crossrefs

Programs

Formula

Equals sec(A001622).
Equals 1/A139346. - Amiram Eldar, Feb 07 2022

Extensions

Offset corrected by Mohammad K. Azarian, Dec 13 2008
Sign in definition added by R. J. Mathar, Feb 05 2009
Previous Showing 31-40 of 73 results. Next