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.

User: David Nguyen

David Nguyen's wiki page.

David Nguyen has authored 12 sequences. Here are the ten most recent ones:

A354709 Decimal expansion of Sum_{p prime} 3*(2p-1)*log(p)/(p^3 + p^2 - 3p + 1).

Original entry on oeis.org

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

Author

David Nguyen, Jun 03 2022

Keywords

Comments

Also logarithmic derivative of A(s,w) at (0,0), where A(s,w) = Product_{p prime} (1 - (1 - (p*(1 - p^(-1-s))^3)/(-1+p))*(1 - (p*(1 - p^(-1-w))^3)/(-1+p))), with A(0,0) = A256392.

Examples

			2.52906617358092992925958712930189459230009223994439976118899256270135780066...
		

Crossrefs

Cf. A256392.

Programs

  • Mathematica
    Block[{$MaxExtraPrecision = 1000},
    Do[CC = Join[{0},
        Series[(3 (-1 + 2 p))/(1 - 3 p + p^2 + p^3) //. p -> 1/x, {x, 0,
           t}][[3]]];
      Print[N[-Sum[
            CC[[k]]*(PrimeZetaP'[k] + Log[2]/2^k), {k, 1, Length[CC]}] + (
          3 (-1 + 2 p) Log[p])/(1 - 3 p + p^2 + p^3) //. p -> 2, 75]], {t,
        1000, 1500, 100}]]
    ratfun = 3*(2*p - 1)/(p^3 + p^2 - 3*p + 1); zetas = 0; ratab = Table[konfun = Simplify[ratfun + c/(p^power - 1)] // Together; coefs = CoefficientList[Numerator[konfun], p]; sol = Solve[Last[coefs] == 0, c][[1]]; zetas = zetas + c*Zeta'[power]/Zeta[power] /. sol; ratfun = konfun /. sol, {power, 2, 20}]; Do[Print[N[Sum[Log[p]*ratfun /. p -> Prime[k], {k, 1, m}] + zetas, 120]], {m, 2000, 20000, 2000}] (* Vaclav Kotesovec, Jun 04 2022 *)

Extensions

More digits from Vaclav Kotesovec, Jun 04 2022

A278398 Number of meanders (walks starting at the origin and ending at any altitude >= 0 that may touch but never go below the x-axis) with n steps from {-3,-2,-1,1,2,3}.

Original entry on oeis.org

1, 3, 15, 75, 400, 2169, 11989, 66985, 377718, 2144290, 12240943, 70193305, 404029950, 2332989921, 13508237399, 78399357623, 455959701700, 2656652705422, 15504203678738, 90614205677898, 530288460288008, 3107012752773125, 18223934202102463, 106996319699099591
Offset: 0

Author

David Nguyen, Nov 20 2016

Keywords

Crossrefs

Programs

  • Mathematica
    frac[ex_] := Select[ex, Exponent[#, x] < 0&];
    seq[n_] := Module[{v, m, p}, v = Table[0, n]; m = Sum[x^i, {i, -3, 3}] - 1; p = 1; v[[1]] = 1; For[i = 2, i <= n, i++, p = p*m // Expand; p = p - frac[p]; v[[i]] = p /. x -> 1]; v];
    seq[24] (* Jean-François Alcover, Jul 01 2018, after Andrew Howroyd *)
  • PARI
    seq(n)={my(v=vector(n), m=sum(i=-3, 3, x^i)-1, p=1); v[1]=1; for(i=2, n, p*=m; p-=frac(p); v[i]=subst(p,x,1)); v} \\ Andrew Howroyd, Jun 27 2018

A278394 Number of positive meanders (walks starting at the origin and ending at any altitude > 0 that never touch or go below the x-axis in between) with n steps from {-2,-1,1,2}.

Original entry on oeis.org

1, 2, 5, 17, 58, 209, 761, 2823, 10557, 39833, 151147, 576564, 2208163, 8486987, 32714813, 126430229, 489685674, 1900350201, 7387530575, 28763059410, 112142791763, 437774109384, 1710883748796, 6693281604018, 26210038447737, 102724200946467, 402925631267151
Offset: 0

Author

David Nguyen, Nov 20 2016

Keywords

Comments

By convention, the empty walk (corresponding to n=0) is considered to be a positive meander.

Programs

  • Mathematica
    frac[ex_] := Select[ex, Exponent[#, x] < 0&];
    seq[n_] := Module[{v, m, p}, v = Table[0, n]; m = Sum[x^i, {i, -2, 2}] - 1; p = 1/x; v[[1]] = 1; For[i = 2, i <= n, i++, p = p*m // Expand; p = p - frac[p]; v[[i]] = p /. x -> 1]; v];
    seq[27] (* Jean-François Alcover, Jul 01 2018, after Andrew Howroyd *)
  • PARI
    seq(n)={my(v=vector(n), m=sum(i=-2, 2, x^i)-1, p=1/x); v[1]=1; for(i=2, n, p*=m; p-=frac(p); v[i]=subst(p,x,1)); v} \\ Andrew Howroyd, Jun 27 2018

A278395 Number of positive meanders (walks starting at the origin and ending at any altitude > 0 that never touch or go below the x-axis in between) with n steps from {-3,-2,-1,1,2,3}.

Original entry on oeis.org

1, 3, 12, 60, 311, 1674, 9173, 51002, 286384, 1620776, 9228724, 52810792, 303447096, 1749612736, 10117583749, 58656027314, 340806249367, 1984018271850, 11569932938192, 67574451148408, 395214184047366, 2314315680481252, 13567587349336459, 79621279809031310
Offset: 0

Author

David Nguyen, Nov 20 2016

Keywords

Comments

By convention, the empty walk (corresponding to n=0) is considered to be a positive meander.

Programs

  • Mathematica
    frac[ex_] := Select[ex, Exponent[#, x] < 0&];
    seq[n_] := Module[{v, m, p}, v = Table[0, n]; m = Sum[x^i, {i, -3, 3}] - 1; p = 1/x; v[[1]] = 1; For[i = 2, i <= n, i++, p = p*m // Expand; p = p - frac[p]; v[[i]] = p /. x -> 1]; v];
    seq[24] (* Jean-François Alcover, Jul 01 2018, after Andrew Howroyd *)
  • PARI
    seq(n)={my(v=vector(n), m=sum(i=-3, 3, x^i)-1, p=1/x); v[1]=1; for(i=2, n, p*=m; p-=frac(p); v[i]=subst(p,x,1)); v} \\ Andrew Howroyd, Jun 27 2018

A278396 Number of positive meanders (walks starting at the origin and ending at any altitude > 0 that never touch or go below the x-axis in between) with n steps from {-4,-3,-2,-1,1,2,3,4}.

Original entry on oeis.org

1, 4, 22, 146, 1013, 7269, 53156, 394154, 2951950, 22279439, 169175927, 1290970376, 9891573310, 76050920691, 586426828071, 4533349152056, 35122039919110, 272634162463779, 2119948044144136, 16509519223752380, 128747868290672353, 1005273235488567875
Offset: 0

Author

David Nguyen, Nov 20 2016

Keywords

Comments

By convention, the empty walk (corresponding to n=0) is considered to be a positive meander.

Programs

  • Mathematica
    frac[ex_] := Select[ex, Exponent[#, x] < 0&];
    seq[n_] := Module[{v, m, p}, v = Table[0, n]; m = Sum[x^i, {i, -4, 4}] - 1; p = 1/x; v[[1]] = 1; For[i = 2, i <= n, i++, p = p*m // Expand; p = p - frac[p]; v[[i]] = p /. x -> 1]; v];
    seq[22] (* Jean-François Alcover, Jul 01 2018, after Andrew Howroyd *)
  • PARI
    seq(n)={my(v=vector(n), m=sum(i=-4, 4, x^i)-1, p=1/x); v[1]=1; for(i=2, n, p*=m; p-=frac(p); v[i]=subst(p,x,1)); v} \\ Andrew Howroyd, Jun 27 2018

A278393 Number of positive meanders (walks starting at the origin and ending at any altitude > 0 that never touch or go below the x-axis in between) with n steps from {-4,-3,-2,-1,0,1,2,3,4}.

Original entry on oeis.org

1, 4, 26, 194, 1521, 12289, 101205, 844711, 7120398, 60477913, 516774114, 4437360897, 38256405777, 330948944639, 2871299293535, 24973776734091, 217690276938940, 1901204163460913, 16632544424086901, 145730139895667887, 1278596503973570665, 11231908572986043199
Offset: 0

Author

David Nguyen, Nov 20 2016

Keywords

Comments

By convention, the empty walk (corresponding to n=0) is considered to be a positive meander.

Programs

  • Mathematica
    frac[ex_] := Select[ex, Exponent[#, x] < 0&];
    seq[n_] := Module[{v, m, p}, v = Table[0, n]; m = Sum[x^i, {i, -4, 4}]; p = 1/x; v[[1]] = 1; For[i = 2, i <= n, i++, p = p*m // Expand; p = p - frac[p]; v[[i]] = p /. x -> 1]; v];
    seq[22] (* Jean-François Alcover, Jul 01 2018, after Andrew Howroyd *)
  • PARI
    seq(n)={my(v=vector(n), m=sum(i=-4, 4, x^i), p=1/x); v[1]=1; for(i=2, n, p*=m; p-=frac(p); v[i]=subst(p,x,1)); v} \\ Andrew Howroyd, Jun 27 2018

A278392 Number of positive meanders (walks starting at the origin and ending at any altitude > 0 that never touch or go below the x-axis in between) with n steps from {-3,-2,-1,0,1,2,3}.

Original entry on oeis.org

1, 3, 15, 87, 530, 3329, 21316, 138345, 906853, 5989967, 39804817, 265812731, 1782288408, 11991201709, 80911836411, 547334588037, 3710610424765, 25204313298581, 171492983631249, 1168638213247713, 7974592724571446, 54484621312318007, 372671912259214487
Offset: 0

Author

David Nguyen, Nov 20 2016

Keywords

Comments

By convention, the empty walk (corresponding to n=0) is considered to be a positive meander.

Programs

  • Mathematica
    frac[ex_] := Select[ex, Exponent[#, x] < 0&];
    seq[n_] := Module[{v, m, p}, v = Table[0, n]; m = Sum[x^i, {i, -3, 3}]; p = 1/x; v[[1]] = 1; For[i = 2, i <= n, i++, p = p*m // Expand; p = p - frac[p]; v[[i]] = p /. x -> 1]; v];
    seq[23] (* Jean-François Alcover, Jul 01 2018, after Andrew Howroyd *)
  • PARI
    seq(n)={my(v=vector(n), m=sum(i=-3, 3, x^i), p=1/x); v[1]=1; for(i=2, n, p*=m; p-=frac(p); v[i]=subst(p,x,1)); v} \\ Andrew Howroyd, Jun 27 2018

A278391 Number of positive meanders (walks starting at the origin and ending at any altitude > 0 that never touch or go below the x-axis in between) with n steps from {-2,-1,0,1,2}.

Original entry on oeis.org

1, 2, 7, 29, 126, 565, 2583, 11971, 56038, 264345, 1254579, 5983628, 28655047, 137697549, 663621741, 3206344672, 15525816066, 75324830665, 366071485943, 1781794374016, 8684511754535, 42381025041490, 207055067487165, 1012617403658500, 4956924278927910
Offset: 0

Author

David Nguyen, Nov 20 2016

Keywords

Comments

By convention, the empty walk (corresponding to n=0) is considered to be a positive meander.

Programs

  • Mathematica
    frac[ex_] := Select[ex, Exponent[#, x] < 0&];
    seq[n_] := Module[{v, m, p}, v = Table[0, n]; m = Sum[x^i, {i, -2, 2}]; p = 1/x; v[[1]] = 1; For[i = 2, i <= n, i++, p = p*m // Expand; p = p - frac[p]; v[[i]] = p /. x -> 1]; v];
    seq[25] (* Jean-François Alcover, Jun 30 2018, after Andrew Howroyd *)
  • PARI
    seq(n)={my(v=vector(n), m=sum(i=-2, 2, x^i), p=1/x); v[1]=1; for(i=2, n, p*=m; p-=frac(p); v[i]=subst(p,x,1)); v} \\ Andrew Howroyd, Jun 27 2018

A277923 Number of positive walks with n steps {-4,-3,-2,-1,1,2,3,4} starting at the origin, ending at altitude 2, and staying strictly above the x-axis.

Original entry on oeis.org

0, 1, 3, 16, 84, 505, 3121, 20180, 133604, 904512, 6224305, 43432093, 306524670, 2184389874, 15695947669, 113595885023, 827299204132, 6058526521135, 44586954104578, 329579179316696, 2445858862779018, 18216235711289695, 136113075865844577, 1020074492384232296
Offset: 0

Author

David Nguyen, Nov 04 2016

Keywords

Crossrefs

A277922 Number of positive walks with n steps {-4,-3,-2,-1,1,2,3,4} starting at the origin, ending at altitude 1, and staying strictly above the x-axis.

Original entry on oeis.org

0, 1, 3, 13, 71, 405, 2501, 15923, 104825, 704818, 4827957, 33549389, 235990887, 1676907903, 12019875907, 86804930199, 630999932585, 4613307289260, 33900874009698, 250257489686870, 1854982039556397, 13800559463237465, 103017222722691145, 771348369563479705
Offset: 0

Author

David Nguyen, Nov 04 2016

Keywords

Crossrefs

Programs

  • Maple
    b:= proc(n, y) option remember; `if`(n=0, `if`(y=1, 1, 0), add
         ((h-> `if`(h<1, 0, b(n-1, h)))(y+d), d=[$-4..-1, $1..4]))
        end:
    a:= n-> b(n, 0):
    seq(a(n), n=0..23);  # Alois P. Heinz, Nov 12 2016
  • Mathematica
    b[n_, y_] := b[n, y] = If[n == 0, If[y == 1, 1, 0], Sum[Function[h, If[h < 1, 0, b[n - 1, h]]][y + d], {d, Join[Range[-4, -1], Range[4]]}]];
    a[n_] := b[n, 0];
    Table[a[n], {n, 0, 23}] (* Jean-François Alcover, Apr 03 2017, after Alois P. Heinz *)