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 1-5 of 5 results.

A380235 Triangle read by rows: T(n,k) is the number of n edge non-orientable genus k maps.

Original entry on oeis.org

1, 4, 2, 19, 16, 8, 106, 137, 128, 47, 709, 1254, 1890, 1372, 473, 5356, 12597, 27036, 31007, 22556, 7190, 44558, 133518, 379491, 611322, 704066, 469632, 144904, 397146, 1464725, 5229092, 11017122, 17691240, 18521632, 11990766, 3534490, 3716039, 16373700, 70805740, 186044902, 387965547, 563764626, 571333104, 352456980, 100895667
Offset: 1

Views

Author

Andrew Howroyd, Jan 17 2025

Keywords

Examples

			Triangle begins:
      1;
      4,      2;
     19,     16,      8;
    106,    137,    128,     47;
    709,   1254,   1890,   1372,    473;
   5356,  12597,  27036,  31007,  22556,   7190;
  44558, 133518, 379491, 611322, 704066, 469632, 144904;
  ...
		

Crossrefs

Main diagonal is A380236.
Cf. A267180 (rooted), A379439 (on orientable surface).

A238396 Triangle T(n,k) read by rows: T(n,k) is the number of rooted genus-k maps with n edges, n>=0, 0<=k<=n.

Original entry on oeis.org

1, 2, 0, 9, 1, 0, 54, 20, 0, 0, 378, 307, 21, 0, 0, 2916, 4280, 966, 0, 0, 0, 24057, 56914, 27954, 1485, 0, 0, 0, 208494, 736568, 650076, 113256, 0, 0, 0, 0, 1876446, 9370183, 13271982, 5008230, 225225, 0, 0, 0, 0, 17399772, 117822512, 248371380, 167808024, 24635754, 0, 0, 0, 0, 0, 165297834, 1469283166, 4366441128, 4721384790, 1495900107, 59520825, 0
Offset: 0

Views

Author

Joerg Arndt, Feb 26 2014

Keywords

Examples

			Triangle starts:
00: 1,
01: 2, 0,
02: 9, 1, 0,
03: 54, 20, 0, 0,
04: 378, 307, 21, 0, 0,
05: 2916, 4280, 966, 0, 0, 0,
06: 24057, 56914, 27954, 1485, 0, 0, 0,
07: 208494, 736568, 650076, 113256, 0, 0, 0, 0,
08: 1876446, 9370183, 13271982, 5008230, 225225, 0, 0, 0, 0,
09: 17399772, 117822512, 248371380, 167808024, 24635754, 0, ...,
10: 165297834, 1469283166, 4366441128, 4721384790, 1495900107, 59520825, 0, ...,
11: 1602117468, 18210135416, 73231116024, 117593590752, 66519597474, 8608033980, 0, ...,
12: 15792300756, 224636864830, 1183803697278, 2675326679856, 2416610807964, 672868675017, 24325703325, 0, ...,
...
		

References

  • David M. Jackson and Terry I. Visentin, An Atlas of the Smaller Maps in Orientable and Nonorientable Surfaces, Chapman & Hall/CRC, circa 2000. See page 227.

Crossrefs

Sum of row n is A000698(n+1).
See A267180 for nonorientable analog.
The triangle without the zeros is A269919.

Programs

  • Mathematica
    T[0, 0] = 1; T[n_, g_] /; g < 0 || g > n/2 = 0; T[n_, g_] := T[n, g] = ((4n - 2)/3 T[n-1, g] + (2n-3)(2n-2)(2n-1)/12 T[n-2, g-1] + 1/2 Sum[(2k-1)(2(n - k)-1) T[k-1, i] T[n-k-1, g-i] , {k, 1, n-1}, {i, 0, g}])/((n+1)/6);
    Table[T[n, g], {n, 0, 10}, {g, 0, n}] // Flatten (* Jean-François Alcover, Jul 19 2018, after Gheorghe Coserea *)
  • PARI
    N=20;
    MEM=matrix(N+1,N+1, r,c, -1);  \\ for memoization
    Q(n,g)=
    {
        if (n<0,  return( (g<=0) ) ); \\ not given in paper
        if (g<0,  return( 0 ) ); \\ not given in paper
        if (n<=0, return( g==0 ) );  \\ as in paper
        my( m = MEM[n+1,g+1] );
        if ( m != -1,  return(m) );  \\ memoized value
        my( t=0 );
        t += (4*n-2)/3 * Q(n-1, g);
        t += (2*n-3)*(2*n-2)*(2*n-1)/12 * Q(n-2, g-1);
        my(l, j);
        t += 1/2*
            sum(k=1, n-1, l=n-k;  \\ l+k == n, both >= 1
                sum(i=0, g, j=g-i;  \\ i+j == g, both >= 0
                    (2*k-1)*(2*l-1) * Q(k-1, i) * Q(l-1, j)
                );
            );
        t *= 6/(n+1);
        MEM[n+1, g+1] = t;  \\ memoize
        return(t);
    }
    for (n=0, N, for (g=0, n, print1(Q(n, g),", "); );  print(); ); /* print triangle */

Formula

From Gheorghe Coserea, Mar 11 2016: (Start)
(n+1)/6 * T(n, g) = (4*n-2)/3 * T(n-1, g) + (2*n-3)*(2*n-2)*(2*n-1)/12 * T(n-2, g-1) + 1/2 * Sum_{k=1..n-1} Sum_{i=0..g} (2*k-1) * (2*(n-k)-1) * T(k-1, i) * T(n-k-1, g-i) for all n >= 1 and 0 <= g <= n/2, with the initial conditions T(0,0) = 1 and T(n,g) = 0 for g < 0 or g > n/2.
For column g, as n goes to infinity we have T(n,g) ~ t(g) * n^(5*(g-1)/2) * 12^n, where t(g) = (A269418(g)/A269419(g)) / (2^(g-2) * gamma((5*g-1)/2)) and gamma is the Gamma function.
(End)

A007137 Number of rooted maps with n edges on the projective plane.

Original entry on oeis.org

1, 10, 98, 982, 10062, 105024, 1112757, 11934910, 129307100, 1412855500, 15548498902, 172168201088, 1916619748084, 21436209373224, 240741065193282, 2713584138389838, 30687358107371442, 348061628432108352
Offset: 1

Views

Author

Keywords

References

  • E. R. Canfield, Calculating the number of rooted maps on a surface, Congr. Numerantium, 76 (1990), 21-34.
  • David M. Jackson and Terry I. Visentin, An Atlas of the Smaller Maps in Orientable and Nonorientable Surfaces, Chapman & Hall/CRC, circa 2000. See page 227.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A006300.
A column of A267180.

Programs

  • Maple
    R:=sqrt(1-12*x): seq(coeff(convert(series(((2*R+1)/3-sqrt(R*(R+2)/3))/(2*x),x,50),polynom),x,n),n=1..25); # Pab Ter, Nov 07 2005
  • Mathematica
    With[{r=Sqrt[1-12x]},Rest[CoefficientList[Series[((2r+1)/3-Sqrt[r (r+2)/3])/ (2x),{x,0,20}],x]]](* Harvey P. Dale, Mar 02 2018 *)
  • PARI
    seq(N) = {
      my(x = 'x + O('x^(N+2)), r=sqrt(1-12*x));
      Vec(((2*r+1)/3 - sqrt(r*(r+2)/3))/(2*x));
    };
    seq(18)
    \\ test: y = 'x*Ser(seq(300),'x); 0 == 9*x^3*y^4 - 6*x^2*y^3 + 2*x*(21*x - 1)*y^2 + (10*x - 1)*y + x
    \\ Gheorghe Coserea, Jul 07 2018
    
  • PARI
    b(n) = sum(k=0, n\2, n!/(k!^2 * (n - 2*k)!)); \\ A002426
    a(n) = 2*sum(k=0, n-1, binomial(2*n, k) * 3^k * b(n-k))/(n+1);
    vector(18, n, a(n)) \\ Gheorghe Coserea, Dec 26 2018

Formula

From Pab Ter (pabrlos2(AT)yahoo.com), Nov 07 2005: (Start)
G.f.: ((2*R+1)/3-sqrt(R*(R+2)/3))/(2*x) where R=sqrt(1-12*x);
a(n) ~ sqrt(3/2)*12^n/(n^(5/4)*GAMMA(3/4)). (End)
From Gheorghe Coserea, Dec 26 2018: (Start)
a(n) = (2/(n+1)) * Sum_{k=0..n-1} binomial(2*n, k) * 3^k * A002426(n-k).
G.f. y=A(x) satisfies:
0 = 9*x^3*y^4 - 6*x^2*y^3 + 2*x*(21*x - 1)*y^2 + (10*x - 1)*y + x.
0 = x*(4*x + 1)*(12*x - 1)^3*y'''' + 4*(132*x^2 + 19*x - 1)*(12*x - 1)^2*y''' + 12*(1476*x^2 + 60*x - 11)*(12*x - 1)*y'' + 72*(2016*x^2 - 117*x - 4)*y' + 648*(16*x - 1)*y.
(End)

Extensions

Reference gives 20 terms
Description corrected May 15 1997, thanks to Jean-Francois Beraud
More terms from Pab Ter (pabrlos2(AT)yahoo.com), Nov 07 2005

A006344 Number of rooted maps with n edges on Klein bottle.

Original entry on oeis.org

4, 84, 1340, 19280, 263284, 3486224, 45247084, 579150012, 7338291224, 92272957568, 1153361204996, 14348020042512, 177803262186064, 2196338193610064, 27057921450352204, 332583930387073712
Offset: 2

Views

Author

Jean-Francois Beraud (beraud(AT)univ-mlv.fr)

Keywords

References

  • David M. Jackson and Terry I. Visentin, An Atlas of the Smaller Maps in Orientable and Nonorientable Surfaces, Chapman & Hall/CRC, circa 2000. See page 227.

Crossrefs

A column of A267180.

A118450 Number of rooted n-edge one-vertex one-face maps on a non-orientable surface (of genus n).

Original entry on oeis.org

1, 4, 41, 488, 8229, 164892, 4016613, 112818960
Offset: 1

Views

Author

Valery A. Liskovets, May 04 2006

Keywords

Comments

One-vertex one-face maps on orientable surfaces are counted by A035319.

References

  • E. R. Canfield, Calculating the number of rooted maps on a surface, Congr. Numerantium, 76 (1990), 21-34.
  • D. M. Jackson and T. I. Visentin, An atlas of the smaller maps in orientable and nonorientable surfaces. CRC Press, Boca Raton, 2001.

Crossrefs

Main diagonal of A267180.
Cf. A035319.

Extensions

a(7)-a(8) added by Andrew Howroyd, Jan 16 2022
Showing 1-5 of 5 results.