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 1-9 of 9 results.

A322013 Square array A(n,k), n >= 1, k >= 1, read by antidiagonals, where A(n,k) is the number of permutations of n copies of 1..k introduced in order 1..k with no element equal to another within a distance of 1.

Original entry on oeis.org

1, 1, 0, 1, 1, 0, 1, 5, 1, 0, 1, 36, 29, 1, 0, 1, 329, 1721, 182, 1, 0, 1, 3655, 163386, 94376, 1198, 1, 0, 1, 47844, 22831355, 98371884, 5609649, 8142, 1, 0, 1, 721315, 4420321081, 182502973885, 66218360625, 351574834, 56620, 1, 0
Offset: 1

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Author

Seiichi Manyama, Nov 24 2018

Keywords

Examples

			Square array begins:
   1, 1,     1,         1,              1,                    1, ...
   0, 1,     5,        36,            329,                 3655, ...
   0, 1,    29,      1721,         163386,             22831355, ...
   0, 1,   182,     94376,       98371884,         182502973885, ...
   0, 1,  1198,   5609649,    66218360625,     1681287695542855, ...
   0, 1,  8142, 351574834, 47940557125969, 16985819072511102549, ...
		

Crossrefs

Main diagonal gives A321666.

Programs

  • PARI
    q(n,x) = sum(i=1, n, (-1)^(n-i) * binomial(n-1, n-i) * x^i/i!)
    T(n,k) = subst(serlaplace(q(n,x)^k), x, 1)/k! \\ Andrew Howroyd, Feb 03 2024

Formula

T(n,k) = A322093(n,k) / k!. - Andrew Howroyd, Feb 03 2024

A190830 Number of permutations of 4 copies of 1..n introduced in order 1..n with no element equal to another within a distance of 1.

Original entry on oeis.org

1, 0, 1, 182, 94376, 98371884, 182502973885, 551248360550999, 2536823683737613858, 16904301142107043464659, 156690501089429126239232946, 1955972150994131850032960933480, 32016987304767134806200915633253966, 672058204939482014438623912695190927357
Offset: 0

Views

Author

R. H. Hardin, May 21 2011

Keywords

Examples

			Some solutions for n=3:
  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1
  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2
  3  1  3  3  1  3  3  3  3  3  3  1  1  3  1  1
  1  2  2  2  2  2  2  1  1  2  1  3  3  1  3  2
  2  3  3  3  1  1  3  2  2  3  2  1  2  3  1  1
  3  2  1  2  3  2  1  3  1  1  3  2  3  2  2  3
  1  3  2  3  2  3  3  1  3  2  2  3  2  1  3  1
  3  2  3  1  3  1  2  3  1  1  1  2  1  3  2  3
  1  1  1  3  1  3  1  2  2  3  3  3  2  2  3  2
  2  3  2  1  3  2  3  1  3  1  1  2  3  3  1  3
  3  1  1  2  2  3  1  3  2  2  2  3  1  1  3  2
  2  3  3  1  3  1  2  2  3  3  3  1  3  2  2  3
		

Crossrefs

Row n=4 of A322013.

Formula

From Vaclav Kotesovec, Nov 24 2018: (Start)
Recurrence: 3*(64*n^3 - 280*n^2 + 414*n - 245)*a(n) = (2048*n^6 - 12032*n^5 + 30400*n^4 - 42608*n^3 + 32484*n^2 - 14624*n + 1731)*a(n-1) + 3*(3840*n^5 - 20640*n^4 + 40104*n^3 - 36340*n^2 + 23378*n - 13429)*a(n-2) - 18*(384*n^4 - 1488*n^3 + 1556*n^2 - 986*n + 649)*a(n-3) - 27*(64*n^3 - 88*n^2 + 46*n - 47)*a(n-4).
a(n) ~ 2^(5*n+1) * n^(3*n) / (3^n * exp(3*n + 3)). (End)

Extensions

a(0)=1 prepended by Seiichi Manyama, Nov 16 2018

A348813 a(n) = number of chord labeled loopless diagrams by number of K_3.

Original entry on oeis.org

0, 1, 22, 1415, 140343, 20167651, 3980871156, 1035707510307, 343866839138005, 141979144588872613, 71386289535825383386, 42954342000612934599071, 30482693813120122213093587, 25196997894058490607106028095, 24001522306527907199721466108488, 26102037346800387738363882455862531
Offset: 1

Views

Author

Michael De Vlieger, Nov 01 2021

Keywords

Crossrefs

Extensions

a(14) onwards from Andrew Howroyd, Feb 05 2024

A193624 Number of ways n triples can sit in a row without any siblings next to each other.

Original entry on oeis.org

1, 0, 72, 37584, 53529984, 152458744320, 766958183193600, 6236531290739312640, 76788695692068062330880, 1361934174627779827740180480, 33454092372947487842682293452800, 1102556254139040688616563751190528000
Offset: 0

Views

Author

Andrew Woods, Aug 01 2011

Keywords

Crossrefs

Programs

  • Magma
    B:=Binomial;
    f:= func< n,j | (&+[B(n,k)*B(2*k,j)*(-3)^(n+k-j): k in [Ceiling(j/2)..n]]) >;
    A193624:= func< n | (&+[Factorial(n+j)*f(n,j): j in [0..2*n]]) >;
    [A193624(n): n in [0..30]]; // G. C. Greubel, Sep 22 2023
    
  • Mathematica
    A193624[n_]:= Sum[(n+j)!*Binomial[n,k]*Binomial[2*k,j]*(-3)^(n+k-j), {j,0,2*n}, {k,Ceiling[j/2],n}];
    Array[A193624, 30, 0] (* G. C. Greubel, Sep 22 2023 *)
  • SageMath
    b=binomial;
    def f(j,n): return sum(b(n,k)*b(2*k,j)*(-3)^(n+k-j) for k in range((j//2),n+1))
    def A193624(n): return sum(factorial(n+j)*f(j,n) for j in range(2*n+1))
    [A193624(n) for n in range(31)] # G. C. Greubel, Sep 22 2023

Formula

Lim_{n -> oo} a(n) -> (3n)!*exp(-2).
a(n) = A190826(n) * 6^n * n! for n >= 1. - Nathaniel Johnston, Aug 01 2011
a(n) -3*(9*n^3-9*n^2+8*n+8)*a(n-1) +108*(n-1)*(n^2-11*n+16)*a(n-2) +3024*(n-1)*(n-2)^2*a(n-3) -5184*(n-1)*(n-2)*(n-3)*a(n-4) = 0. - R. J. Mathar, May 23 2014
a(n) = Sum_{j=0..2*n} Sum_{k=ceiling(j/2)..n} (n+j)! * binomial(2*k, j) * binomial(n, k) * (-3)^(n+k-j). - G. C. Greubel, Sep 22 2023

A193638 Number of permutations of the multiset {1,1,1,2,2,2,3,3,3,...,n,n,n} with no two consecutive terms equal.

Original entry on oeis.org

1, 0, 2, 174, 41304, 19606320, 16438575600, 22278418248240, 45718006789687680, 135143407245840698880, 553269523327347306412800, 3039044104423605600086688000, 21819823367694505460651694873600, 200345011881335747639978525387827200
Offset: 0

Views

Author

Andrew Woods, Aug 01 2011

Keywords

Examples

			a(2) = 2 because there are two permutations of {1,1,1,2,2,2} avoiding equal consecutive terms: 121212 and 212121.
		

Crossrefs

Cf. A114938 = similar, with two copies instead of three.
Cf. A193624 = arrangements of triples with no adjacent siblings.
Cf. A190826.

Programs

  • Magma
    B:=Binomial;
    f:= func< n,j | (&+[B(n,k)*B(2*k,j)*(-3)^(k-j): k in [Ceiling(j/2)..n]]) >;
    A193638:= func< n | (-1/2)^n*(&+[Factorial(n+j)*f(n,j): j in [0..2*n]]) >;
    [A193638(n): n in [0..30]]; // G. C. Greubel, Sep 22 2023
    
  • Maple
    a:= proc(n) option remember; `if`(n<3, (n-1)*(3*n-2)/2,
        n*((3*n-1)*(3*n^2-5*n+4) *a(n-1) +2*(n-1)*(6*n^2-9*n-1) *a(n-2)
        -4*n*(n-1)*(n-2) *a(n-3))/(2*n-2))
        end:
    seq(a(n), n=0..20);  # Alois P. Heinz, Jun 05 2013
  • Mathematica
    a[n_]:= (1/6^n)*Sum[(n+j)!*Binomial[n, k]*Binomial[2k, j]*(-3)^(n+k-j), {j,0,2n}, {k, Ceiling[j/2], n}]; Table[a[n], {n, 0, 13}] (* Jean-François Alcover, Jul 22 2017, after Tani Akinari *)
  • Maxima
    a(n):= (1/6^n)*sum((n+j)!*sum(binomial(n,k)*binomial(2*k,j)* (-3)^(n+k-j), k,ceiling(j/2),n), j,0,2*n); /* Tani Akinari, Sep 23 2012 */
    
  • Python
    from sympy.core.cache import cacheit
    @cacheit
    def a(n): return (n-1)*(3*n-2)//2 if n<3 else n*((3*n-1)*(3*n**2 - 5*n + 4)*a(n-1) + 2*(n-1)*(6*n**2 -9*n-1)*a(n-2) - 4*n*(n-1)*(n-2)*a(n- 3))//(2*n-2)
    print([a(n) for n in range(51)]) # Indranil Ghosh, Jul 22 2017, formula after Maple code
    
  • SageMath
    b=binomial;
    def f(j,n): return sum(b(n,k)*b(2*k,j)*(-3)^(k-j) for k in range((j//2),n+1))
    def A193638(n): return (-1/2)^n*sum(factorial(n+j)*f(j,n) for j in range(2*n+1))
    [A193638(n) for n in range(31)] # G. C. Greubel, Sep 22 2023

Formula

a(n) = A190826(n) * n! for n >= 1.
a(n) = A193624(n)/6^n.
a(n) = Sum_{s+t+u=n} (-1)^t*multinomial(n;s,t,u)*(3*s+2*t+u)!/(3!)^s. - Alexis Martin, Nov 16 2017
a(n) = (1/6^n) * Sum_{j=0..2*n} Sum_{k=ceiling(j/2)..n} (n+j)! * binomial(2*k, j) * binomial(n, k) * (-3)^(n+k-j). - Tani Akinari, Sep 23 2012
a(n) = n*( (3*n-1)*(3*n^2-5*n+4)*a(n-1) +2*(n-1)*(6*n^2-9*n-1)*a(n-2) -4*n*(n-1)*(n-2)*a(n-3) )/(2*n-2). - Alois P. Heinz, Jun 05 2013

A321666 Number of arrangements of n 1's, n 2's, ..., n n's avoiding equal consecutive terms and introduced in ascending order.

Original entry on oeis.org

1, 1, 1, 29, 94376, 66218360625, 16985819072511102549, 2421032324142610480402567434373, 271259741131895052775392614041761701799270286, 32119646666355552112999645991677870426882424139287301894021793
Offset: 0

Views

Author

Seiichi Manyama, Nov 16 2018

Keywords

Crossrefs

Programs

  • PARI
    {a(n) = sum(i=n, n^2, i!*polcoef(sum(j=1, n, (-1)^(n-j)*binomial(n-1, j-1)*x^j/j!)^n, i))/n!} \\ Seiichi Manyama, May 27 2019

Formula

a(n) = A321634(n)/n!.
a(n) ~ exp(5/12) * n^((n-1)*(2*n-1)/2) / (2*Pi)^(n/2). - Vaclav Kotesovec, Nov 24 2018

A321669 Number of permutations of 9 copies of 1..n introduced in order 1..n with no element equal to another within a distance of 1.

Original entry on oeis.org

1, 0, 1, 2872754, 104650147201049, 23575497690601916022516, 24302858067615766089801166488125, 91155245844064069307740171414201519055298, 1046031892354833895113128900608177633584652958677057, 32119646666355552112999645991677870426882424139287301894021793
Offset: 0

Views

Author

Seiichi Manyama, Nov 16 2018

Keywords

Crossrefs

Formula

a(n) ~ 9^(7*n + 1/2) * n^(8*n) / (4480^n * exp(8*(n+1))). - Vaclav Kotesovec, Nov 24 2018

A321670 Number of permutations of 10 copies of 1..n introduced in order 1..n with no element equal to another within a distance of 1.

Original entry on oeis.org

1, 0, 1, 20824778, 7279277647839552, 19672658572012343899666292, 293736218147318801678882792470437721, 18739368045280595665934917472507368174737872589, 4204427313459831775866154680419213479057724331798640498651
Offset: 0

Views

Author

Seiichi Manyama, Nov 16 2018

Keywords

Comments

In general, for r > 1, row r of A322013 is asymptotic to r^(r*n + 1/2) * n^((r-1)*n) / ((r!)^n * exp((r-1)*(n+1))). - Vaclav Kotesovec, Nov 24 2018

Crossrefs

Formula

a(n) ~ 2^(2*n + 1/2) * 5^(8*n + 1/2) * n^(9*n) / (567^n * exp(9*(n+1))). - Vaclav Kotesovec, Nov 24 2018

A348814 a(n) = number of loopless diagrams by number of K_3 up to rotational symmetry.

Original entry on oeis.org

0, 1, 4, 126, 9367, 1120780, 189565588, 43154533233, 12735808866899, 4732638168795171, 2163220895025390670, 1193176166690983987122, 781607533669746761791541
Offset: 1

Views

Author

Michael De Vlieger, Nov 01 2021

Keywords

Crossrefs

Showing 1-9 of 9 results.