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 1-4 of 4 results.

A061160 Numerators in expansion of Euler transform of b(n) = 1/3.

Original entry on oeis.org

1, 1, 5, 50, 215, 646, 8711, 25475, 105925, 3091270, 11691247, 36809705, 445872155, 1364113925, 5085042010, 50975292560, 183383680088, 588817265695, 19512559194875, 62369303509475, 224877933068647, 2214198452392027, 7686538660149565, 25124342108522750
Offset: 0

Views

Author

Vladeta Jovovic, Apr 17 2001

Keywords

Comments

Denominators of c(n) are 3^d(n), where d(n)=power of 3 in (3*n)!, cf. A004128.

Crossrefs

Programs

  • Maple
    b:= proc(n) option remember; `if`(n=0, 1, add(add(
          d/3, d=numtheory[divisors](j))*b(n-j), j=1..n)/n)
        end:
    a:= n-> numer(b(n)):
    seq(a(n), n=0..30);  # Alois P. Heinz, Jul 28 2017
  • Mathematica
    c[n_] := c[n] = If[n == 0, 1,
         (1/(3n)) Sum[c[n-k] DivisorSigma[1, k], {k, 1, n}]];
    a[n_] := Numerator[c[n]];
    Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Apr 24 2022 *)

Formula

Numerators of c(n), where c(n) = (1/(3*n))*Sum_{k=1..n} c(n-k)*sigma(k), n>0, c(0)=1.

A061161 Numerators in expansion of Euler transform of b(n) = 1/4.

Original entry on oeis.org

1, 1, 13, 55, 1235, 4615, 55801, 200343, 8977475, 36804235, 367235363, 1444888289, 32062742231, 120729974115, 1205864254225, 5201022002071, 395884671433315, 1603069490974835, 15989295873680415, 64312573140322525, 1250332447587844829, 5262481040435242585
Offset: 0

Views

Author

Vladeta Jovovic, Apr 17 2001

Keywords

Comments

Denominators of c(n) are 2^A004134(n).

Crossrefs

Programs

  • Maple
    b:= proc(n) option remember; `if`(n=0, 1, add(add(
          d/4, d=numtheory[divisors](j))*b(n-j), j=1..n)/n)
        end:
    a:= n-> numer(b(n)):
    seq(a(n), n=0..30);  # Alois P. Heinz, Jul 28 2017
  • Mathematica
    c[n_] := c[n] = If[n == 0, 1,
         (1/(4n)) Sum[c[n-k] DivisorSigma[1, k], {k, 1, n}]];
    a[n_] := Numerator[c[n]];
    Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Apr 24 2022 *)

Formula

Numerators of c(n), where c(n) = (1/(4*n))*Sum_{k=1..n} c(n-k)*sigma(k), n>0, c(0)=1.

A343204 Numerators of coefficients in expansion of Product_{k>=1} (1 + x^k)^(1/2).

Original entry on oeis.org

1, 1, 3, 13, 67, 239, 1031, 2501, 36579, 109915, 468653, 1043851, 9395751, 21232827, 97493519, 235880373, 7717800611, 17385733651, 82456426833, 175398844079, 1578297716013, 3634938193489, 15867173716609, 34517119775523, 619312307079687, 1363237700933583
Offset: 0

Views

Author

Ilya Gutkovskiy, Apr 07 2021

Keywords

Examples

			1, 1/2, 3/8, 13/16, 67/128, 239/256, 1031/1024, 2501/2048, 36579/32768, 109915/65536, 468653/262144, 1043851/524288, ...
		

Crossrefs

Cf. A000009, A022567, A046161 (denominators), A061159, A098987.

Programs

  • Maple
    b:= proc(n) option remember; `if`(n=0, 1, add(b(n-j)*add(
         `if`(d::odd, d/2, 0), d=numtheory[divisors](j)), j=1..n)/n)
        end:
    a:= n-> numer(b(n)):
    seq(a(n), n=0..25);  # Alois P. Heinz, Apr 12 2021
  • Mathematica
    nmax = 25; CoefficientList[Series[Product[(1 + x^k)^(1/2), {k, 1, nmax}], {x, 0, nmax}], x] // Numerator
    a[n_] := a[n] = If[n == 0, 1, (1/(2 n)) Sum[Sum[Mod[d, 2] d, {d, Divisors[k]}] a[n - k], {k, 1, n}]]; Table[a[n], {n, 0, 25}] // Numerator

Formula

a(n) / A046161(n) ~ exp(sqrt(n/6)*Pi) / (4*3^(1/4)*n^(3/4)). - Vaclav Kotesovec, Apr 12 2021

A282030 Numerators in an "almost partition identity".

Original entry on oeis.org

1, 1, 19, 343, 11305, 58349, 3230255, 15652637, 1076842043, 55727585675, 827556357229, 4462381098539, 472784126720165, 2370070888522337, 36233114985867725, 676572663482064349, 76896411800028508843, 428831636633480067995, 60264676461386071468577
Offset: 0

Views

Author

N. J. A. Sloane, Feb 19 2017

Keywords

Crossrefs

Showing 1-4 of 4 results.