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 1-3 of 3 results.

A274279 Expansion of e.g.f.: tanh(x*W(x)), where W(x) = LambertW(-x)/(-x).

Original entry on oeis.org

1, 2, 7, 40, 341, 3936, 57107, 992384, 20025385, 459466240, 11804134079, 335571265536, 10456512176189, 354362575314944, 12975301760361163, 510462668072058880, 21472710312090391889, 961728814178702327808, 45692671937666739799799, 2295278998002033651875840, 121545436687537993689631525, 6767130413049423041105231872, 395177438856180565803457658627, 24152146710231984411570685870080
Offset: 1

Views

Author

Paul D. Hanna, Jun 19 2016

Keywords

Examples

			E.g.f.: A(x) = x + 2*x^2/2! + 7*x^3/3! + 40*x^4/4! + 341*x^5/5! + 3936*x^6/6! + 57107*x^7/7! + 992384*x^8/8! + 20025385*x^9/9! + 459466240*x^10/10! + 11804134079*x^11/11! + 335571265536*x^12/12! +...
such that A(x) = tanh(x*W(x))
where W(x) = LambertW(-x)/(-x) begins
W(x) = 1 + x + 3*x^2/2! + 16*x^3/3! + 125*x^4/4! + 1296*x^5/5! + 16807*x^6/6! + 262144*x^7/7! + 4782969*x^8/8! + 100000000*x^9/9! +...+ (n+1)^(n-1)*x^n/n! +...
and satisfies W(x) = exp(x*W(x)).
Also, A(x) = (W(x)^2 - 1)/(W(x)^2 + 1), where
W(x)^2 = 1 + 2*x + 8*x^2/2! + 50*x^3/3! + 432*x^4/4! + 4802*x^5/5! + 65536*x^6/6! + 1062882*x^7/7! + 20000000*x^8/8! +...+ 2*(n+2)^(n-1)*x^n/n! +...

Links

Crossrefs

Cf. A000272, A195136, A238085, A264902, A274278, A277468, A277480.

Programs

  • Mathematica
    Rest[CoefficientList[Series[(LambertW[-x]^2 - x^2)/(LambertW[-x]^2 + x^2), {x, 0, 20}], x] * Range[0, 20]!] (* Vaclav Kotesovec, Jun 23 2016 *)
Rest[With[{nmax=30}, CoefficientList[Series[Tanh[-LambertW[-x]], {x,0,nmax}], x]*Range[0, nmax]!]] (* G. C. Greubel, Feb 19 2018 *)
  • PARI
    {a(n) = my(W=sum(m=0, n, (m+1)^(m-1)*x^m/m!) +x*O(x^n)); n!*polcoeff(tanh(x*W), n)}
for(n=1, 30, print1(a(n), ", "))
  • PARI
    {a(n) = my(W = sum(m=0, n, (m+1)^(m-1)*x^m/m!) +x*O(x^n)); n!*polcoeff( (W^2 - 1)/(W^2 + 1), n)}
for(n=1, 30, print1(a(n), ", "))
  • PARI
    x='x+O('x^30); Vec(serlaplace(tanh(-lambertw(-x)))) \\ G. C. Greubel, Feb 19 2018

Formula

E.g.f.: (W(x)^2 - 1)/(W(x)^2 + 1), where W(x) = LambertW(-x)/(-x) = exp(x*W(x)) = Sum_{n>=0} (n+1)^(n-1)*x^n/n!.
a(n) ~ 4*exp(2) * n^(n-1) / (1+exp(2))^2. - Vaclav Kotesovec, Jun 23 2016
a(n) = Sum_{k=0..n-1} (-1)^k * A264902(n,k). - Alois P. Heinz, Aug 08 2022

A274278 a(n) = ((n+1)^(n-1) - (n-1)^(n-1))/2 for n>=1.

Original entry on oeis.org

1, 0, 1, 6, 49, 520, 6841, 107744, 1979713, 41611392, 985263601, 25958682112, 753424361713, 23888905963520, 821659980883561, 30472793606184960, 1212264580564478209, 51496393511442350080, 2326573297949232710881, 111398795962351731212288, 5635038492335356268228401, 300285949343202022103973888, 16814498551154751682934232601, 987042812055984079330393194496
Offset: 0

Views

Author

Paul D. Hanna, Jun 19 2016

Keywords

Examples

			E.g.f.: A(x) = 1 + x^2/2! + 6*x^3/3! + 49*x^4/4! + 520*x^5/5! + 6841*x^6/6! + 107744*x^7/7! + 1979713*x^8/8! + 41611392*x^9/9! + 985263601*x^10/10! +...
such that A(x) = cosh(x*W(x))
where W(x) = LambertW(-x)/(-x) begins
W(x) = 1 + x + 3*x^2/2! + 16*x^3/3! + 125*x^4/4! + 1296*x^5/5! + 16807*x^6/6! + 262144*x^7/7! + 4782969*x^8/8! + 100000000*x^9/9! +...+ (n+1)^(n-1)*x^n/n! +...
and satisfies W(x) = exp(x*W(x)).
Also, A(x) = (W(x) + 1/W(x))/2 where
1/W(x) = 1 - x - x^2/2! - 4*x^3/3! - 27*x^4/4! - 256*x^5/5! - 3125*x^6/6! - 46656*x^7/7! - 823543*x^8/8! +...+ -(n-1)^(n-1)*x^n/n! +...

Crossrefs

Cf. A000272, A195136, A274279.

Programs

  • PARI
    {a(n) = ((n+1)^(n-1) - (n-1)^(n-1))/2}
for(n=0,30,print1(a(n),", "))
  • PARI
    {a(n) = sum(k=0,(n-1)\2, binomial(n-1,2*k+1) * n^(n-2*k-2))}
for(n=0,30,print1(a(n),", "))
  • PARI
    {a(n) = my(W=sum(m=0,n, (m+1)^(m-1)*x^m/m!) +x*O(x^n)); n!*polcoeff(cosh(x*W),n)}
for(n=0,30,print1(a(n),", "))

Formula

E.g.f.: cosh(x*W(x)) = (W(x) + 1/W(x))/2 where W(x) = LambertW(-x)/(-x) = exp(x*W(x)) = Sum_{n>=0} (n+1)^(n-1)*x^n/n!.
a(n) = Sum_{k=0..floor((n-1)/2)} C(n-1,2*k+1) * n^(n-2*k-2).

A277499 E.g.f.: -sin(LambertW(-x)).

Original entry on oeis.org

0, 1, 2, 8, 52, 476, 5646, 82368, 1426888, 28623376, 652516090, 16660233600, 470930272572, 14598765522368, 492441140292934, 17955574113204224, 703714660937658128, 29500170665998713088, 1317136516654501334898, 62399954043306802391040
Offset: 0

Views

Author

Vaclav Kotesovec, Oct 18 2016

Keywords

Links

Crossrefs

Cf. A195136, A277461, A277498.

Programs

  • Maple
    S:= series(-sin(LambertW(-x)),x,31):
seq(coeff(S,x,n)*n!, n=0..30); # Robert Israel, Oct 30 2016
  • Mathematica
    CoefficientList[Series[-Sin[LambertW[-x]], {x, 0, 20}], x] * Range[0, 20]!
  • PARI
    x='x+O('x^50); concat([0], Vec(serlaplace(-sin(lambertw(-x))))) \\ G. C. Greubel, Nov 08 2017

Formula

a(n) ~ cos(1) * n^(n-1).
Showing 1-3 of 3 results.

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