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 10 results.

A122399 a(n) = Sum_{k=0..n} k^n * k! * Stirling2(n,k).

Original entry on oeis.org

1, 1, 9, 211, 9285, 658171, 68504709, 9837380491, 1863598406805, 450247033371451, 135111441590583909, 49300373690091496171, 21495577955682021043125, 11037123350952586270549531, 6591700149366720366704735109
Offset: 0

Views

Author

Vladeta Jovovic, Aug 31 2006

Keywords

Comments

Conjecture: Let p be prime. The sequence obtained by reducing a(n) modulo p for n >= 1 is purely periodic with period p - 1. For example, modulo 7 the sequence becomes [1, 2, 1, 3, 3, 0, 1, 2, 1, 3, 3, 0, ...], with an apparent period of 6. Cf. A338040. - Peter Bala, May 31 2022

Examples

			E.g.f.: A(x) = 1 + x + 9*x^2/2! + 211*x^3/3! + 9285*x^4/4! + 658171*x^5/5! + ...
such that
A(x) = 1 + (exp(x)-1) + (exp(2*x)-1)^2 + (exp(3*x)-1)^3 + (exp(4*x)-1)^4 + ...
The e.g.f. is also given by the series:
A(x) = 1/2 + exp(x)/(1+exp(x))^2 + exp(4*x)/(1+exp(2*x))^3 + exp(9*x)/(1+exp(3*x))^4 + exp(16*x)/(1+exp(4*x))^5 + exp(25*x)/(1+exp(5*x))^6 + ...
or, equivalently,
A(x) = 1/2 + exp(-x)/(1+exp(-x))^2 + exp(-2*x)/(1+exp(-2*x))^3 + exp(-3*x)/(1+exp(-3*x))^4 + exp(-4*x)/(1+exp(-4*x))^5 + exp(-5*x)/(1+exp(-5*x))^6 + ...
		

Crossrefs

Programs

  • Maple
    a := n -> add(k^n*k!*combinat[stirling2](n,k),k=0..n); # Max Alekseyev, Feb 01 2007
  • Mathematica
    Flatten[{1,Table[Sum[k^n*k!*StirlingS2[n,k],{k,0,n}],{n,1,20}]}] (* Vaclav Kotesovec, Jun 21 2013 *)
  • PARI
    {a(n)=polcoeff(sum(m=0, n, m^m*m!*x^m/prod(k=1, m, 1-m*k*x+x*O(x^n))), n)}
    for(n=0, 20, print1(a(n), ", ")) \\ Paul D. Hanna, Jan 05 2013
    
  • PARI
    {a(n)=n!*polcoeff(sum(k=0, n, (exp(k*x +x*O(x^n)) - 1)^k), n)}
    for(n=0,25,print1(a(n),", ")) \\ Paul D. Hanna, Oct 26 2014
    
  • PARI
    /* From e.g.f. infinite series: */
    \p100 \\ set precision
    {A=Vec(serlaplace(sum(n=0, 500, 1.*exp(n^2*x +O(x^26))/(1 + exp(n*x +O(x^26)))^(n+1)) ))}
    for(n=0, #A-1, print1(round(A[n+1]), ", ")) \\ Paul D. Hanna, Oct 30 2014

Formula

E.g.f.: Sum_{n >= 0} (exp(n*x) - 1)^n. - Vladeta Jovovic, Sep 03 2006
E.g.f.: Sum_{n>=0} exp(n^2*x) / (1 + exp(n*x))^(n+1). - Paul D. Hanna, Oct 26 2014
E.g.f.: Sum_{n>=0} exp(-n*x) / (1 + exp(-n*x))^(n+1). - Paul D. Hanna, Oct 30 2014
O.g.f.: Sum_{n>=0} n^n * n! * x^n / Product_{k=1..n} (1 - n*k*x). - Paul D. Hanna, Jan 05 2013
Limit n->infinity (a(n)/n!)^(1/n)/n = ((1+exp(1/r))*r^2)/exp(1) = A317855/exp(1) = 1.162899527477400818845..., where r = 0.87370243323966833... is the root of the equation 1/(1+exp(-1/r)) = -r*LambertW(-exp(-1/r)/r). - Vaclav Kotesovec, Jun 21 2013
a(n) ~ c * A317855^n * (n!)^2 / sqrt(n), where c = 0.327628285569869481442286492410507030710253054522608... - Vaclav Kotesovec, Aug 09 2018
Let A(x) = 1 + x + 9*x^2/2! + 211*x^3/3! + ... denote the e.g.f. of the sequence. Let F(x) denote the series reversion of A(x) - 1 = x - 9*x^2/2 + 16*x^3/3 - 205*x^4/4 - 2714*x^5/5 - .... Then both dF/dx = 1 - 9*x + 16*x^2 - 205*x^3 - 2714*x^4 - ... and exp(F(x)) = 1 + x - 4*x^2 + x^3 - 38*x^4 - 606*x^5 - ... have integer coefficients. Note that 1 + series reversion(exp(F(x)) - 1) is the o.g.f. for A122400. - Peter Bala, Aug 09 2022

Extensions

More terms from Max Alekseyev, Feb 01 2007

A249459 a(n) = Sum_{k=0..n} k^(2*n).

Original entry on oeis.org

1, 1, 17, 794, 72354, 10874275, 2438235715, 762963987380, 317685943157892, 169842891165484965, 113394131858832552133, 92465351109879998121806, 90431265068257318469676710, 104479466717230437574945525959, 140782828210237288756752539959687
Offset: 0

Views

Author

Vaclav Kotesovec, Oct 29 2014

Keywords

Crossrefs

Programs

  • Mathematica
    Table[Sum[k^(2*n),{k,1,n}],{n,1,20}]
    Table[n!*SeriesCoefficient[Sum[Exp[k^2*x], {k, 1, n}],{x,0,n}], {n,1,20}]
  • PARI
    a(n)=n!*polcoeff(sum(k=0, n, exp(k*x+x*O(x^n))^k), n);
    for(n=1, 20, print1(a(n), ", "))
    
  • PARI
    my(N=20, x='x+O('x^N)); Vec(sum(k=0, N, (k^2*x)^k/(1-k^2*x))) \\ Seiichi Manyama, Dec 03 2021

Formula

E.g.f.: Sum_{n>=0} exp(n^2*x).
a(n) ~ exp(2)/(exp(2)-1) * n^(2*n).
G.f.: Sum_{k>=0} (k^2 * x)^k/(1 - k^2 * x). - Seiichi Manyama, Dec 03 2021

Extensions

a(0)=1 prepended by Seiichi Manyama, Dec 03 2021

A338040 E.g.f.: Sum_{j>=0} 4^j * (exp(j*x) - 1)^j.

Original entry on oeis.org

1, 4, 132, 11140, 1763076, 449262724, 168055179012, 86720706877060, 59029852191779076, 51241585497612147844, 55245853646893977682692, 72423868722672448652558980, 113447698393867318106045295876, 209271794145089904620369489016964
Offset: 0

Views

Author

Vaclav Kotesovec, Oct 08 2020

Keywords

Comments

In general, if k > 0 and e.g.f.: Sum_{j>=0} k^j * (exp(j*x) - 1)^j, then a(n) ~ c * (1 + k*exp(1/r))^n * r^(2*n) * n!^2 / sqrt(n), where r is the root of the equation exp(1/r) * (1 + 1/(r*LambertW(-exp(-1/r)/r))) = -1/k and c is a constant (dependent only on k).
Conjecture: Let p be prime. The sequence obtained by reducing a(n) modulo p for n >= 1 is purely periodic with period p - 1. For example, modulo 7 the sequence becomes [4, 6, 3, 0, 1, 0, 4, 6, 3, 0, 1, 0, 4, 6, 3, 0, 1, 0, ...], with an apparent period of 6. - Peter Bala, May 31 2022

Crossrefs

Programs

  • Mathematica
    Flatten[{1, Table[Sum[4^j * j^n * j! * StirlingS2[n, j], {j, 0, n}], {n, 1, 20}]}]
    nmax = 20; CoefficientList[Series[1 + Sum[4^j*(Exp[j*x] - 1)^j, {j, 1, nmax}], {x, 0, nmax}], x] * Range[0, nmax]!
  • PARI
    {a(n)=local(X=x+x*O(x^n)); n!*polcoeff(sum(m=0, n, 4^m*(exp(m*X)-1)^m), n)}

Formula

a(n) = Sum_{j=0..n} 4^j * j^n * j! * Stirling2(n,j).
a(n) ~ c * (1 + 4*exp(1/r))^n * r^(2*n) * n!^2 / sqrt(n), where r = 0.95894043087329419322124137165060249611787608513866855417024... is the root of the equation exp(1/r) * (1 + 1/(r*LambertW(-exp(-1/r)/r))) = -1/4 and c = 0.37483929689722634406486945426531890297038414869116425498643733178324...

A221077 E.g.f.: Sum_{n>=0} tanh(n*x)^n.

Original entry on oeis.org

1, 1, 8, 160, 5888, 345856, 29677568, 3502489600, 544181977088, 107675615297536, 26435436140822528, 7885689342279024640, 2809177794704769548288, 1177952320402008693538816, 574318105367992485583781888, 322156963576521588458420961280, 206009256195720974104252003647488
Offset: 0

Views

Author

Paul D. Hanna, Dec 31 2012

Keywords

Comments

Conjecture: Let p be prime. The sequence obtained by reducing a(n) modulo p for n >= 1 is purely periodic with period p - 1. For example, modulo 7 the sequence becomes [1, 1, 6, 1, 0, 4, 1, 1, 6, 1, 0, 4, 1, 1, 6, 1, 0, 4 ...], with an apparent period of 6. - Peter Bala, Jun 01 2022

Examples

			E.g.f.: A(x) = 1 + x + 8*x^2/2! + 160*x^3/3! + 5888*x^4/4! + 345856*x^5/5! +...
where
A(x) = 1 + tanh(x) + tanh(2*x)^2 + tanh(3*x)^3 + tanh(4*x)^4 + tanh(5*x)^5 +...
		

Crossrefs

Programs

  • Mathematica
    nmax = 20; CoefficientList[Series[1 + Sum[Tanh[k*x]^k, {k, 1, nmax}], {x, 0, nmax}], x] * Range[0, nmax]! (* Vaclav Kotesovec, May 31 2022 *)
    Join[{1}, Table[Sum[2^n * k^n * Sum[(-1)^j * Binomial[k, j] * Sum[(-1)^m * Binomial[j + m - 1, m] * StirlingS2[n, m] * m! / 2^m, {m, 1, n}], {j, 0, k}], {k, 0, n}], {n, 1, 20}]] (* Vaclav Kotesovec, Jun 01 2022 *)
  • PARI
    {a(n)=local(X=x+x*O(x^n), Egf); Egf=sum(m=0, n, tanh(m*X)^m); n!*polcoeff(Egf, n)}
    for(n=0,20,print1(a(n),", ") )
    
  • PARI
    {a(n)=local(X=x+x*O(x^n), Egf); Egf=sum(m=0, n, (exp(2*m*X)-1)^m/(exp(2*m*X)+1)^m); n!*polcoeff(Egf, n)}
    for(n=0,20,print1(a(n),", ") )

Formula

E.g.f.: Sum_{n>=0} (exp(2*n*x) - 1)^n / (exp(2*n*x) + 1)^n.
a(n) ~ c * 2^n * (n!)^2 / (sqrt(n) * (log(1+sqrt(2)))^(2*n)), where c = 0.521427744491499132141002572969819345522922990165233786929882335275903215... - Vaclav Kotesovec, Nov 05 2014, updated Jun 02 2022

A221078 E.g.f.: Sum_{n>=0} tan(n*x)^n.

Original entry on oeis.org

1, 1, 8, 164, 6400, 404176, 37541888, 4814990144, 815074508800, 176018678814976, 47223034903789568, 15407438848482919424, 6007522256082907955200, 2758698201106509138251776, 1473586749521302260021198848, 905915791153129699969076117504
Offset: 0

Views

Author

Paul D. Hanna, Dec 31 2012

Keywords

Comments

Conjecture: Let p be prime. The sequence obtained by reducing a(n) modulo p for n >= 1 is purely periodic. If p = 4*m + 1 the period appears to be p - 1, while if p = 4*m + 3 the period appears to be 2*(p - 1). Cf. A245322. - Peter Bala, Jun 01 2022

Examples

			E.g.f.: A(x) = 1 + x + 8*x^2/2! + 164*x^3/3! + 6400*x^4/4! + 404176*x^5/5! +...
where
A(x) = 1 + tan(x) + tan(2*x)^2 + tan(3*x)^3 + tan(4*x)^4 + tan(5*x)^5 +...
		

Crossrefs

Programs

  • Mathematica
    nmax = 20; CoefficientList[Series[1 + Sum[Tan[k*x]^k, {k, 1, nmax}], {x, 0, nmax}], x] * Range[0, nmax]! (* Vaclav Kotesovec, May 31 2022 *)
    Join[{1}, Table[Sum[(-1)^((n-k)/2) * 2^n * k^n * Sum[(-1)^j * Binomial[k, j] * Sum[(-1)^m * Binomial[j + m - 1, m] * StirlingS2[n, m] * m! / 2^m, {m, 1, n}], {j, 0, k}], {k, 0, n}], {n, 1, 20}]] (* Vaclav Kotesovec, Jun 01 2022 *)
  • PARI
    {a(n)=local(X=x+x*O(x^n), Egf); Egf=sum(m=0, n, tan(m*X)^m); n!*polcoeff(Egf, n)}
    for(n=0,20,print1(a(n),", ") )

Formula

a(n) ~ c * d^n * (n!)^2 / sqrt(n), where d = 2.82830192319144609189890882712268369027077465204866199572119508594067235975..., c = 0.3460492649810724519960613805096579760009441161242336020188358769124140... - Vaclav Kotesovec, Nov 05 2014, updated Jun 02 2022

A245322 E.g.f.: Sum_{n>=0} sin(n*x)^n.

Original entry on oeis.org

1, 1, 8, 161, 6016, 360421, 31628288, 3823725821, 609263681536, 123729353398441, 31195066498285568, 9560281195915697081, 3500145542231863853056, 1508772905238685631514061, 756360258034794813559144448, 436312320288025061112662937941, 286966475921556619941746443288576
Offset: 0

Views

Author

Vaclav Kotesovec, Nov 05 2014

Keywords

Comments

It appears that for n >= 1, a(2*n) is even and a(2*n-1) is odd. Conjecture: Let p be prime. The sequence obtained by reducing a(n) modulo p for n >= 1 is purely periodic. If p = 4*m + 1 the period appears to be p - 1, while if p = 4*m + 3 the period appears to be 2*(p - 1). Cf. A224899 and A221078. - Peter Bala, May 31 2022

Crossrefs

Programs

  • Mathematica
    nmax=20; Flatten[{1,Rest[CoefficientList[Series[Sum[Sin[k*x]^k, {k, 1, nmax}], {x, 0, nmax}], x] * Range[0, nmax]!]}]
    Flatten[{1,Table[Sum[(-1)^k * (n-2*k)^n * 2^(2*k-n) * Sum[Binomial[n-2*k,j] * (-1)^j * (n-2*k-2*j)^n,{j,0,n-2*k}],{k,0,n/2}],{n,1,20}]}]
  • PARI
    {a(n)=n!*polcoeff(sum(k=0, n, sin(k*x+x*O(x^n))^k), n)}
    for(n=0, 20, print1(a(n), ", "))

Formula

a(n) ~ c * d^n * (n!)^2 / sqrt(n), where d = 2.6508143537621057095493599669955786931108630276472035393383790812849064745..., c = 0.447880926276318254580767843378566025547642779941081708311676940459098... - Vaclav Kotesovec, Nov 05 2014, updated Jun 02 2022

A195415 E.g.f.: Sum_{n>=1} tanh(n*x)^n = Sum_{n>=1} a(n)*4^(n-1)*x^n/n!.

Original entry on oeis.org

1, 2, 10, 92, 1351, 28982, 855100, 33214232, 1642999501, 100843185962, 7520379392890, 669760178257172, 70211429619908851, 8558006664633638942, 1200128210993564085880, 191861070874818576596912, 34685967730611200643509401, 7041037426518318365605795922
Offset: 1

Views

Author

Paul D. Hanna, Sep 17 2011

Keywords

Comments

Conjecture: Let p be prime. The sequence obtained by reducing a(n) modulo p is purely periodic with period p - 1. For example, modulo 7 the sequence becomes [1, 2, 3, 1, 0, 2, 1, 2, 3, 1, 0, 2, 1, 2, 3, 1, 0, 2, ...], with an apparent period of 6. - Peter Bala, May 29 2022

Examples

			E.g.f.: A(x) = x + 8*x^2/2! + 160*x^3/3! + 5888*x^4/4! + 345856*x^5/5! +...
or, equivalently,
A(x) = x + 2*4*x^2/2! + 10*4^2*x^3/3! + 92*4^3*x^4/4! + 1351*4^4*x^5/5! +...
where
A(x) = tanh(x) + tanh(2*x)^2 + tanh(3*x)^3 + tanh(4*x)^4 + tanh(5*x)^5 +...
		

Crossrefs

Programs

  • Maple
    seq(coeff(n!/4^(n-1)*series(add(tanh(n*x)^n, n = 1..100), x, 101), x, n), n = 1..100); # Peter Bala, May 29 2022
  • Mathematica
    nmax = 20; Rest[CoefficientList[Series[Sum[Tanh[k*x]^k, {k, 1, nmax}], {x, 0, nmax}], x] * Range[0, nmax]! / 4^(Range[0, nmax] - 1)] (* Vaclav Kotesovec, May 31 2022 *)
  • PARI
    {a(n)=local(X=x+x*O(x^n), Egf); Egf=sum(m=1, n, tanh(m*X)^m); n!/4^(n-1)*polcoeff(Egf, n)}

Formula

E.g.f.: Sum_{n>=1} ( 1 - 2/(1+exp(2*n*x)) )^n = Sum_{n>=1} a(n)*4^(n-1)/n!.
a(n) ~ c * d^n * n^(2*n + 1/2), where d = 1 / (2 * exp(2) * log(1+sqrt(2))^2) = 0.0871085887239583895519632137900851584739951067757899616766024190... and c = 13.10490857177911562030370300610447966745088413236135355214718... - Vaclav Kotesovec, May 31 2022
a(n) = A221077(n) / 4^(n-1). - Vaclav Kotesovec, Jun 02 2022

A249489 a(n) = [x^n/n!] Sum_{k=0..n} cosh(k*x)^k.

Original entry on oeis.org

1, 0, 9, 0, 12070, 0, 126447741, 0, 5100496997940, 0, 562605048135059545, 0, 138523311740417986721274, 0, 66543520389763227261554370645, 0, 56664734898911130799849838608991176, 0, 79610326854782816434044397510470501877041
Offset: 0

Views

Author

Vaclav Kotesovec, Oct 30 2014

Keywords

Crossrefs

Programs

  • Mathematica
    Flatten[{1,Table[Sum[Sum[Binomial[k,j] * k^n*(k-2*j)^n / 2^k,{j,0,k}],{k,0,n}],{n,1,20}]}]
  • PARI
    {a(n)=n!*polcoeff(sum(k=0, n, cosh(k*x+x*O(x^n))^k), n)}
    for(n=0, 20, print1(a(n), ", "))
    
  • PARI
    {a(n) = sum(k=0,n,sum(j=0,k, binomial(k, j) * k^n*(k-2*j)^n / 2^k ))}
    for(n=0, 20, print1(a(n), ", ")) \\ Paul D. Hanna, Oct 15 2018, using Vaclav's formula.

Formula

a(n) = Sum_{k=0..n} Sum_{j=0..k} binomial(k, j) * k^n * (k-2*j)^n / 2^k. [Explicitly stating Vaclav's formula in Mma program - Paul D. Hanna, Oct 15 2018]
If n is even, then a(n) ~ c * (1-2*r)^n * n^(2*n) / (2^n * exp(n) * (r*(1-r))^(n/2)), where r = 0.0832217201995176507819192648878903254298041... is the root of the equation (r/(1-r))^(1-2*r) = exp(-2), and c = 2.09233700490262732901066903251002074102409436600891921766318742438...

Extensions

Name clarified by Paul D. Hanna, Oct 15 2018

A249698 E.g.f.: Sum_{n>=0} Product_{k=1..n} cosh(k*x).

Original entry on oeis.org

1, 0, 6, 0, 2426, 0, 7553776, 0, 90192976308, 0, 2939813898295990, 0, 213701821328573755046, 0, 30292525174041077292043440, 0, 7609302838629919155170452856136, 0, 3152886110080180503361685427596189430, 0, 2038143533263759863560759054752335955960482
Offset: 0

Views

Author

Vaclav Kotesovec, Nov 04 2014

Keywords

Crossrefs

Programs

  • Mathematica
    Table[n!*SeriesCoefficient[Sum[Product[Cosh[k*x],{k,1,j}],{j,0,n}],{x,0,n}],{n,0,20}]
    nn=20; tab = ConstantArray[0,nn]; tab[[1]] = Series[Cosh[x],{x,0,nn}]; Do[tab[[k]] = Series[tab[[k-1]]*Cosh[k*x],{x,0,nn}],{k,2,nn}]; Flatten[{1,Table[kk!*Sum[Coefficient[tab[[k]],x^kk],{k,1,kk}],{kk,1,nn}]}] (* more efficient *)
  • PARI
    {a(n)=local(X=x+x*O(x^n), Egf); Egf=sum(m=0, n, prod(k=1, m, cosh(k*X))); n!*polcoeff(Egf, n)}
    for(n=0, 20, print1(a(n), ", "))

Formula

If n is even a(n) ~ c * d^n * n^(2*n) / (2^(2*n-2) * exp(2*n)), where d = 8.9061971328050809899679389417314..., c = 1.243878632396819914960247452516...

A320419 E.g.f.: Sum_{n>=0} 2^n * sinh(n*x)^n.

Original entry on oeis.org

1, 2, 32, 1298, 98816, 12116642, 2181373952, 541793612978, 177515752718336, 74174630255081282, 38495436789222735872, 24292625097918019749458, 18317925825330618728185856, 16266073932645598088605425122, 16800468023465020621665905672192, 19969924961381649826994229325322738
Offset: 0

Views

Author

Paul D. Hanna, Oct 14 2018

Keywords

Comments

Given e.g.f. A(x),
(1) A(log(1+x)) is the g.f. of A319466,
(1) A(-log(1-x)) is the g.f. of A319947.

Examples

			E.g.f.: A(x) = 1 + 2*x + 32*x^2/2! + 1298*x^3/3! + 98816*x^4/4! + 12116642*x^5/5! + 2181373952*x^6/6! + 541793612978*x^7/7! + ...
such that
A(x) = 1 + 2*sinh(x) + 4*sinh(2*x)^2 + 8*sinh(3*x)^3 + 16*sinh(4*x)^4 +...
or, equivalently,
A(x) = 1 + exp(x)*(1 - exp(-2*x)) + exp(4*x)*(1 - exp(-4*x))^2 + exp(9*x)*(1 - exp(-6*x))^3 + exp(16*x)*(1 - exp(-8*x))^4 + exp(25*x)*(1 - exp(-10*x))^5 + ...
RELATED SERIES.
A(log(1+x)) = 1 + 2*x + 15*x^2 + 201*x^3 + 3807*x^4 + 93103*x^5 + 2788528*x^6 + 98816388*x^7 + 4043274742*x^8 + ... + A319466(n)*x^n + ...
A(-log(1-x)) = 1 + 2*x + 17*x^2 + 233*x^3 + 4457*x^4 + 109599*x^5 + 3294200*x^6 + 117023348*x^7 + 4796944724*x^8 + ... + A319947(n)*x^n + ...
		

Crossrefs

Programs

  • PARI
    {a(n) = n! * polcoeff(sum(k=0, n, 2^k * sinh(k*x + x*O(x^n))^k ), n)}
    for(n=0, 30, print1(a(n), ", "))

Formula

E.g.f.: Sum_{n>=0} exp(n^2*x) * (1 - exp(-2*n*x))^n.
a(n) = (n!)^2 * [(x*y)^n] 1 / (1 - exp(x + y) + exp(x - y)). - Ilya Gutkovskiy, Apr 24 2025
a(n) ~ n!^2 * c * d^n / sqrt(n), where d = 5.4666049332127684665699843922982444983683628264... and c = 0.390468512121689057564560997910519445284386310369... - Vaclav Kotesovec, Apr 24 2025
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