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: Rigoberto Florez

Rigoberto Florez's wiki page.

Rigoberto Florez has authored 30 sequences. Here are the ten most recent ones:

A378383 Number of subwords of the form UDDD in nondecreasing Dyck paths of length 2*n.

Original entry on oeis.org

0, 0, 0, 1, 5, 19, 64, 202, 612, 1803, 5206, 14809, 41650, 116114, 321478, 885169, 2426462, 6627499, 18048088, 49026874, 132901176, 359625015, 971639014, 2621683741, 7065545950, 19022080034, 51163908874, 137499581917, 369235213742, 990822728623, 2657069356996
Offset: 0

Author

Rigoberto Florez, Nov 24 2024

Keywords

Comments

A Dyck path is nondecreasing if the y-coordinates of its valleys form a nondecreasing sequence.

Programs

  • Mathematica
    Table[If[n < 3, 0, (1/5)((n-3)LucasL[2n-5]+LucasL[2n-3]+Fibonacci[2n+2]-5(n+5) 2^(n-4))], {n,0,26}]

Formula

a(n) =((n-3)*L(2n-5)+L(2n-3)+F(2n+2) -5*(n+5)*2^(n-4))/5 for n>=3, where F(n) = A000045(n) and L(n) = A000032(n).
G.f.: (-x^5+2 x^4-5 x^3+8 x^2-5 x+1)*x^3/(2 x^3-7 x^2+5 x-1)^2.

A377867 Number of subwords of the form DDDD in nondecreasing Dyck paths of length 2n.

Original entry on oeis.org

0, 0, 0, 0, 1, 7, 33, 131, 473, 1608, 5242, 16567, 51123, 154793, 461525, 1358646, 3957088, 11420995, 32707809, 93040751, 263113505, 740238852, 2073098086, 5782387855, 16070206191, 44516728277, 122956408493, 338707969266, 930787894348, 2552224341403, 6984100641117
Offset: 0

Author

Rigoberto Florez, Nov 10 2024

Keywords

Comments

A Dyck path is nondecreasing if the y-coordinates of its valleys form a nondecreasing sequence.

Crossrefs

Programs

  • Mathematica
    Table[If[n < 3, 0, (3*(n-2)*LucasL[2*n-4]-3*Fibonacci[2*n+1])/5+(n+9)*2^(n-4)], {n,0,20}]

Formula

a(n) = (3*(n-2)*L(2*n-4) - 3*F(2*n+1))/5 + (n+9)*2^(n-4) for n>=3, where F(n) = A000045(n) and L(n) = A000032(n).
G.f.: x^4*(1 - 3*x + 2*x^2 + x^4)/((1 - 2*x)^2*(1 - 3*x + x^2)^2).

A377866 Number of subwords of the form DUUD or DDUUD in nondecreasing Dyck paths of length 2n.

Original entry on oeis.org

0, 0, 0, 1, 5, 18, 59, 185, 564, 1685, 4957, 14406, 41455, 118321, 335400, 945193, 2650229, 7398330, 20573219, 57013865, 157517532, 433993661, 1192779085, 3270835566, 8950887895, 24448816993, 66665369424, 181489721425, 493361278949
Offset: 0

Author

Rigoberto Florez, Nov 10 2024

Keywords

Comments

A Dyck path is nondecreasing if the y-coordinates of its valleys form a nondecreasing sequence.

Crossrefs

Programs

  • Mathematica
    Table[If[n<3,0,(2*n*LucasL[2*n-5]-6*Fibonacci[2*n-6]-Fibonacci[2*n-7])/5], {n,0,20}]

Formula

a(n) = (2*n*L(2*n-5) - 6*F(2*n-6) - F(2*n-7))/5 for n>=3, where F(n)=A000045(n) and L(n)=A000032(n).
G.f.: -x^3*(x^2+x-1)/ (x^2-3*x+1)^2.
E.g.f.: exp(3*x/2)*(5*(35 - 8x)*cosh(sqrt(5)*x/2) - sqrt(5)*(79 - 20*x)*sinh(sqrt(5)*x/2))/25 - 7 - x. - Stefano Spezia, Nov 10 2024

A377857 Number of subwords of the form UUUD in nondecreasing Dyck paths of length 2n.

Original entry on oeis.org

0, 0, 0, 1, 5, 18, 60, 191, 589, 1775, 5257, 15360, 44394, 127171, 361595, 1021693, 2871245, 8031246, 22372344, 62096135, 171797257, 473928875, 1304007889, 3579517116, 9804791910, 26804181643, 73145473655, 199276078201, 542076556949, 1472491141770, 3994615719732
Offset: 0

Author

Rigoberto Florez, Nov 09 2024

Keywords

Comments

A Dyck path is nondecreasing if the y-coordinates of its valleys form a nondecreasing sequence.

Crossrefs

Programs

  • Mathematica
    Table[If[n<3,0,n Fibonacci[2n-5]-LucasL[2n-6]], {n,0,30}]

Formula

a(n) = n*F(2*n-5) - L(2*n-6) for n>=3, where F(n) = A000045(n) and L(n) = A000032(n).
G.f.: x^3*(1 - x)^2*(1 + x)/(1 - 3*x + x^2)^2.
a(n) = A317408(n-2)-A317408(n-3) = A030267(n-2)+A030267(n-3). - R. J. Mathar, Dec 16 2024

A377670 Number of subwords of the form UDD in nondecreasing Dyck paths of length 2n.

Original entry on oeis.org

0, 0, 1, 4, 14, 45, 138, 411, 1200, 3454, 9836, 27779, 77938, 217493, 604222, 1672246, 4613030, 12689265, 34817418, 95320335, 260436588, 710278318, 1933906496, 5257545599, 14273273314, 38699274665, 104799960058, 283487736166, 766045036730, 2067997219629, 5577597593466, 15030365074659, 40470488092008
Offset: 0

Author

Rigoberto Florez, Nov 03 2024

Keywords

Comments

A Dyck path is nondecreasing if the y-coordinates of its valleys form a nondecreasing sequence.
a(n) also represents the number of subwords of the form UUDDD in nondecreasing Dyck paths of length 2n.

Crossrefs

Programs

  • Mathematica
    Table[If[n<2, 0,(2*Fibonacci[2n-3] + n*LucasL[2n-3]+2 LucasL[2n-2]-5*2^(n-2))/5], {n,0,20}]

Formula

a(n) = (2*F(2*n-3) + n*L(2*n-3) + 2*L(2*n-2) - 5*2^(n-2))/5 for n>=2, where F(n) = A000045(n) and L(n) = A000032(n).
G.f.: x^2*(1-x)*(x^3-2*x^2+3*x-1)/((2*x-1)*(x^2-3*x+1)^2). - Alois P. Heinz, Nov 03 2024
E.g.f.: (4*exp(3*x/2)*(5*(10 - x)*cosh(sqrt(5)*x/2) - sqrt(5)*(18 - 5*x)*sinh(sqrt(5)*x/2)) - 25*(7 + exp(2*x) + 2*x))/100. - Stefano Spezia, Mar 04 2025

A377679 Number of subwords of the form DDD in nondecreasing Dyck paths of length 2n.

Original entry on oeis.org

0, 0, 0, 1, 6, 26, 97, 333, 1085, 3411, 10448, 31376, 92773, 270907, 783003, 2243815, 6383550, 18048494, 50755897, 142067625, 396014681, 1099863867, 3044737100, 8404071596, 23135752141, 63538808311, 174120317367, 476207551183
Offset: 0

Author

Rigoberto Florez, Nov 03 2024

Keywords

Comments

A Dyck path is nondecreasing if the y-coordinates of its valleys form a nondecreasing sequence.

Crossrefs

Programs

  • Mathematica
    Table[If[n<2,0,n Fibonacci[2 n-3]-LucasL[2 n-2]+2^(n-2)],{n,0,30}]

Formula

a(n) = n*F(2*n-3) - L(2*n-2) + 2^(n-2) for n>=2, where F(n) = A000045(n) and L(n) = A000032(n).
G.f.: x^3*(1 - 2*x + x^2 - x^3)/((1 - 2*x)*(1 - 3*x + x^2)^2).

A375995 Number of subwords of the form UUUU in nondecreasing Dyck paths of length 2n.

Original entry on oeis.org

0, 0, 0, 0, 1, 7, 30, 109, 365, 1164, 3593, 10835, 32106, 93845, 271321, 777432, 2211025, 6248479, 17562870, 49132669, 136884293, 379975140, 1051356761, 2900587115, 7981564866, 21911096357, 60021530545, 164095925424, 447823729825, 1220105286199, 3319124711118
Offset: 0

Author

Rigoberto Florez, Nov 03 2024

Keywords

Comments

A Dyck path is nondecreasing if the y-coordinates of its valleys form a nondecreasing sequence.

Crossrefs

Programs

  • Mathematica
    Table[If[n<=2,0,(2(n-3)LucasL[2n-5]-3Fibonacci[2n-6])/5], {n,0,30}]

Formula

a(n) = (2(n-3)*L(2 n-5)-3F(2n-6))/5 for n>=3 and a(n) = 0 for n<=2, F(.) is a Fibonacci number, L(.) is a Lucas number.
G.f.: x^4*(-x^2+x+1)/(x^2-3x+1)^2.

A360932 Primes of the form H(m,k) = F(k+1)*F(m-k+2) - F(k)*F(m-k+1), where F(m) is the m-th Fibonacci number and m >= 0, 0 <= k <= m.

Original entry on oeis.org

2, 3, 5, 7, 11, 13, 23, 29, 37, 41, 47, 89, 97, 103, 107, 157, 167, 173, 199, 233, 443, 521, 733, 1597, 1741, 1867, 1871, 1877, 2207, 3037, 3571, 7841, 7919, 7951, 9349, 11933, 12823, 28657, 33503, 50549, 54277, 54287, 54293, 54319, 54497, 55717, 142099
Offset: 1

Author

Rigoberto Florez, Feb 25 2023

Keywords

Comments

This sequence appears in the triangle A108038 in this order (reading by rows): 3, 2, 7, 5, 11, 13, 29, 23, 47, 37, 41, 97, 107, 103, 89, 199, 157, 173, 167.
Are there infinitely many primes of the form H(m,k)?
This sequence appears within the determinant Hosoya triangle.

Examples

			29 is a term because it is prime and A108038(8,2) = H(8,2) = 29.  Also A108038(8,7) = H(8,7) = 29.
		

Crossrefs

Cf. A000040, A000045, A005478 (subsequence), A108038, A153892, A067331.

Programs

  • Maple
    Res:= {}:
    M:= 50: # for terms <= F(M)
    fmax:= combinat:-fibonacci(M):
    T[1]:= [1,1]:
    T[2]:= [1,3,1]:
    for i from 3 to M do
      t1:= [op(T[i-1][1..i-1] + T[i-2][1..i-1]),T[i-1][i],0];
      t2:= ListTools:-Reverse(t1);
      T[i]:= zip(max,t1,t2);
      Res:= Res union convert(select(t -> t <= fmax and isprime(t), T[i][1..ceil((i+1)/2)]),set)
    od:
    sort(convert(Res,list)); # Robert Israel, Mar 14 2024
  • Mathematica
    H[r_, k_] := Det[{{Fibonacci[r-k+2], Fibonacci[r-k+1]}, {Fibonacci[k], Fibonacci[k+1]}}];  DeterminantPrimes[t_, m_] :=  Table[If[PrimeQ[H[r,k]],H[r,k], Unevaluated[Sequence[]]], {r,t,m}, {k,1,Ceiling[r/2]}]; ListOfPrimes[t_,m_]:=  Sort[DeleteDuplicates[Flatten[DeterminantPrimes[t, m]]]]; ListOfPrimes[2, 100]
    Select[Union[Flatten[Table[Fibonacci[k+1]Fibonacci[m-k+2]-Fibonacci[k]Fibonacci[m-k+1],{m,0,40},{k,0,m}]]],PrimeQ] (* Harvey P. Dale, Aug 14 2025 *)

Formula

Intersection of A000040 and A108038.

A338588 a(n)/A002939(n+1) is the Kirchhoff index of the disjoint union of two complete graphs each on n and n+1 vertices with the empty graph on n+1 vertices.

Original entry on oeis.org

2, 77, 334, 881, 1826, 3277, 5342, 8129, 11746, 16301, 21902, 28657, 36674, 46061, 56926, 69377, 83522, 99469, 117326, 137201, 159202, 183437, 210014, 239041, 270626, 304877, 341902, 381809, 424706, 470701, 519902
Offset: 0

Author

Rigoberto Florez, Nov 07 2020

Keywords

Comments

Equivalently, the graph can be described as the graph on 3*n + 2 vertices with labels 0..3*n+1 and with i and j adjacent iff i+j>0 mod 3.
These graphs are cographs.
The initial term a(0) = 2 has been included to agree with the formula. For the graph, is not defined.

Examples

			The adjacency matrix of the graph associated with n = 2 is:
  [0, 1, 0, 0, 0, 1, 1, 1]
  [1, 0, 0, 0, 0, 1, 1, 1]
  [0, 0, 0, 1, 1, 1, 1, 1]
  [0, 0, 1, 0, 1, 1, 1, 1]
  [0, 0, 1, 1, 0, 1, 1, 1]
  [1, 1, 1, 1, 1, 0, 0, 0]
  [1, 1, 1, 1, 1, 0, 0, 0]
  [1, 1, 1, 1, 1, 0, 0, 0].
a(2) = 334 because the Kirchhoff index of the graph is 334/30=334/A002939(3).
The first few Kirchhoff indices (n >= 1) as reduced fractions are 77/12, 167/15, 881/56, 913/45, 3277/132, 2671/91, 8129/240, 5873/153, 16301/380, 10951/231.
		

Crossrefs

Programs

  • Mathematica
    Table[(18n^3+37n^2+20n+2), {n,0,30}]

Formula

a(n) = 18*n^3 + 37*n^2 + 20*n + 2.
G.f.: (2 + 69*x + 38*x^2 - x^3)/(x - 1)^4.
E.g.f.: exp(x)*(2 + 75*x + 91*x^2 + 18*x^3). - Stefano Spezia, Nov 08 2020
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4). - Wesley Ivan Hurt, Nov 08 2020

A338527 Number of spanning trees in the join of the disjoint union of two complete graphs each on n and n+1 vertices with the empty graph on n+1 vertices.

Original entry on oeis.org

24, 13500, 34420736, 239148450000, 3520397039081472, 94458953432730437824, 4179422085120000000000000, 283894102615246085842939590912, 28059580711858187192007680000000000, 3870669526565955444680027453177986243584
Offset: 1

Author

Rigoberto Florez, Nov 07 2020

Keywords

Comments

Equivalently, the graph can be described as the graph on 3*n + 2 vertices with labels 0..3*n+1 and with i and j adjacent iff i+j> 0 mod 3.
These graphs are cographs.

Examples

			The adjacency matrix of the graph associated with n = 2 is: (compare A204437)
 [0, 1, 0, 0, 0, 1, 1, 1]
 [1, 0, 0, 0, 0, 1, 1, 1]
 [0, 0, 0, 1, 1, 1, 1, 1]
 [0, 0, 1, 0, 1, 1, 1, 1]
 [0, 0, 1, 1, 0, 1, 1, 1]
 [1, 1, 1, 1, 1, 0, 0, 0]
 [1, 1, 1, 1, 1, 0, 0, 0]
 [1, 1, 1, 1, 1, 0, 0, 0]
a(2) = 13500 because the graph has 13500 spanning trees.
		

Crossrefs

Programs

  • Mathematica
    Table[(n + 1)*(2 n + 2)^n*(2 n + 1)^(2 n - 1), {n, 1, 10}]

Formula

a(n) = (n + 1)*(2 n + 2)^n*(2 n + 1)^(2 n - 1).

Extensions

Offset changed by Georg Fischer, Nov 03 2023