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 11-19 of 19 results.

A247042 Decimal expansion of delta_2 (negated), a constant associated with a certain two-dimensional lattice sum.

Original entry on oeis.org

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

Views

Author

Jean-François Alcover, Sep 10 2014

Keywords

Comments

This constant is named sigma(1/2) in the Borwein reference.

Examples

			-3.900264920001955882845475336604973219209047856477537388...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Sections 1.10 Madelung's constant, p. 79.

Crossrefs

Programs

  • Mathematica
    delta2 = 2*Zeta[1/2]*(Zeta[1/2, 1/4] - Zeta[1/2, 3/4]); RealDigits[delta2, 10, 102] // First
  • PARI
    2*zeta(1/2)*(zetahurwitz(1/2,1/4)-zetahurwitz(1/2,3/4)) \\ Charles R Greathouse IV, Jan 31 2018

Formula

delta_2 = 2*zeta(1/2)*(zeta(1/2, 1/4) - zeta(1/2, 3/4)), where zeta(s,a) gives the generalized Riemann zeta function.

A182565 Decimal expansion of Madelung constant (negated) for cuprous oxide Cu_2O.

Original entry on oeis.org

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

Views

Author

N. J. A. Sloane, May 05 2012

Keywords

Examples

			-4.4424752098389...
		

Crossrefs

Formula

Equals (sqrt(3)/4) * (2 * A085469 + 3 * (A185577 + A185578)). [Sakamoto] - Andrey Zabolotskiy, Oct 12 2023

Extensions

More terms using the formula added by Andrey Zabolotskiy, Oct 12 2023

A182566 Decimal expansion of Madelung constant (negated) for zinc sulfide ZnS.

Original entry on oeis.org

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

Views

Author

N. J. A. Sloane, May 05 2012

Keywords

Comments

This constant is for sphalerite, the more common polymorph of zinc sulfide. - Jon E. Schoenfield, Mar 11 2018
The sphalerite (zincblende) structure consists of two interpenetrating face-centered cubic lattices of ions with charges +2 and -2, together occupying all sites of the diamond structure. This constant does not include overall factor 2 from the absolute value of the charges. This constant is normalized to the nearest neighbor distance, not the lattice constant; cf. the values 3.782926104 (or 3.78292610408577750878 from Sarkar & Bhattacharyya) and 7.56584 from pages 41 and 16 of "Lattice Sums Then and Now", which equal 4/sqrt(3) and 8/sqrt(3) times this constant. - Andrey Zabolotskiy, Feb 18 2021

Examples

			-1.6380550533887...
		

Crossrefs

Formula

Equals (sqrt(3)/4) * A085469 + (1/2) * A181152. [Glasser] - Andrey Zabolotskiy, Oct 12 2023

Extensions

More terms based on Sarkar & Bhattacharyya and Steiger et al. added by Andrey Zabolotskiy, Jul 16 2023
More terms using the formula added by Andrey Zabolotskiy, Oct 12 2023

A182567 Decimal expansion of Madelung constant (negated) for calcium fluoride CaF_2.

Original entry on oeis.org

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

Views

Author

N. J. A. Sloane, May 05 2012

Keywords

Examples

			-5.0387848798...
		

Crossrefs

Formula

This constant = sqrt(3)/2 * A085469 + 2 * A181152. [Glasser] - Andrey Zabolotskiy, Oct 12 2023

Extensions

More terms using the formula added by Andrey Zabolotskiy, Oct 12 2023

A264156 Decimal expansion of M_5, the 5-dimensional analog of Madelung's constant (negated).

Original entry on oeis.org

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

Views

Author

Jean-François Alcover, Nov 06 2015

Keywords

Examples

			-1.9093378156187685595201437984336...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Sections 1.10 Madelung's constant, p. 77.

Crossrefs

Programs

  • Mathematica
    digits = 32; f[n_, x_] := 1/Sqrt[Pi*x]*(EllipticTheta[4, 0, Exp[-x]]^n - 1); M[5] = NIntegrate[f[5, x], {x, 0, Infinity}, WorkingPrecision -> digits + 5]; RealDigits[M[5], 10, digits] // First

Formula

Equals (1/sqrt(Pi))*Integral_{t=0..oo} ((Sum_{k=-oo..oo} (-1)^k*exp(-k^2*t))^5 - 1)/sqrt(t) dt.

A264157 Decimal expansion of M_7, the 7-dimensional analog of Madelung's constant (negated).

Original entry on oeis.org

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

Views

Author

Jean-François Alcover, Nov 06 2015

Keywords

Examples

			-2.01240598979798606439503063580430044165678065812192932878490469117330...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Sections 1.10 Madelung's constant, p. 77.

Crossrefs

Programs

  • Mathematica
    digits = 32; f[n_, x_] := 1/Sqrt[Pi*x]*(EllipticTheta[4, 0, Exp[-x]]^n - 1); M[7] = NIntegrate[f[7, x], {x, 0, Infinity}, WorkingPrecision -> digits + 5]; RealDigits[M[7], 10, digits] // First
  • PARI
    th4(x)=1+2*sumalt(n=1,(-1)^n*x^n^2)
    intnum(x=0,[oo,1], (th4(exp(-x))^7-1)/sqrt(Pi*x)) \\ Charles R Greathouse IV, Jun 06 2016

Formula

Equals (1/sqrt(Pi))*Integral_{t=0..oo} ((Sum_{k=-oo..oo} (-1)^k*exp(-k^2*t))^7-1)/sqrt(t) dt.

Extensions

More terms from Charles R Greathouse IV, Jun 06 2016

A336275 Decimal expansion of the dimensionless coefficient of the Coulomb self-energy of a uniformly charged two-dimensional square.

Original entry on oeis.org

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

Views

Author

Amiram Eldar, Jul 15 2020

Keywords

Comments

Coulomb self-energy of a system of electric charges is the total electrostatic potential energy of interaction between charge elements.
For a uniformly charged two-dimensional square with a total charge Q and a side length L it is equal to c * k*Q^2/L, where k is the Coulomb constant (A182999) and c is this constant.

Examples

			1.486604799123689351264092833819785899009872739605305...
		

Crossrefs

Programs

  • Mathematica
    RealDigits[2*(1 - Sqrt[2])/3 + 2*Log[1 + Sqrt[2]], 10, 100][[1]]
  • PARI
    2*(1 - sqrt(2))/3 + 2 * log(1 + sqrt(2)) \\ Michel Marcus, Jul 15 2020

Formula

Equals 2*(1 - sqrt(2))/3 + 2 * log(1 + sqrt(2)).

A246966 Decimal expansion of H_2, the analog of Madelung's constant for the planar hexagonal lattice.

Original entry on oeis.org

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

Views

Author

Jean-François Alcover, Sep 10 2014

Keywords

Comments

The ionic hexagonal (triangular) lattice considered here consists of three interpenetrating hexagonal lattices of ions with charges +1, -1, 0. Equivalently, one may consider the honeycomb net consisting of two hexagonal lattices of ions with charges +1 and -1 (the h-BN layer structure). In any case, this lattice sum is based on the nearest neighbor distance (not the length of the period of the ionic crystal structure, which is sqrt(3) times greater). - Andrey Zabolotskiy, Jun 21 2022

Examples

			1.54221972170650525853141576436424529561948...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Sections 1.10 Madelung's constant, p. 78.

Crossrefs

Programs

  • Mathematica
    H2 = (-3 + Sqrt[3])*Zeta[1/2]*((1 - Sqrt[2])*Zeta[1/2, 1/3] + Zeta[1/2, 1/6]); RealDigits[H2, 10, 103] // First
  • PARI
    (sqrt(3)-3)*zeta(1/2)*((1-sqrt(2))*zetahurwitz(1/2, 1/3) + zetahurwitz(1/2, 1/6)) \\ Charles R Greathouse IV, Jan 31 2018

Formula

H_2 = (-3 + sqrt(3))*zeta(1/2)*((1 - sqrt(2))*zeta(1/2, 1/3) + zeta(1/2, 1/6)), where zeta(s,a) gives the generalized Riemann zeta function.

A271872 Decimal expansion of the doubly infinite sum N_3 = Sum_{i,j,k = -inf..inf} (-1)^(i+j+k)/(i^2+j^2+k^2), a lattice constant analog of Madelung's constant (negated).

Original entry on oeis.org

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

Views

Author

Jean-François Alcover, Apr 24 2016

Keywords

Examples

			-2.51935615208944531334271172732943791211649913675173257750066...
		

References

  • Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 1.10 Madelung's constant, p. 77.

Crossrefs

Cf. A088537 (M_2), A085469 (M_3), A090734 (M_4), A086054 (N_2).

Programs

  • Mathematica
    digits = 101; Clear[s]; s[max_] := s[max] = NSum[(-1)^n Csch[Pi *Sqrt[m^2 + 2 n^2]]/Sqrt[m^2 + 2 n^2], {m, 1, max}, {n, 1, max}, Method -> "AlternatingSigns", WorkingPrecision -> digits + 10]; s[10]; s[max = 20]; Print[max]; While[RealDigits[s[max], 10, digits + 5][[1]] != RealDigits[s[max/2], 10, digits + 5][[1]], max = max*2; Print[max]]; N3 = Pi^2/3 - Pi*Log[2] - Pi/Sqrt[2] Log[2 (Sqrt[2] + 1)] + 8 Pi*s[max]; RealDigits[N3, 10, digits][[1]]

Formula

N_3 = Pi^2/3-Pi*log(2)-(Pi/sqrt(2))*log(2(sqrt(2)+1))+8 Pi*Sum_{m,n >= 1} (-1)^n csch(Pi*sqrt(m^2+2n^2))/sqrt(m^2+2n^2).
Previous Showing 11-19 of 19 results.