A057977 -id:A057977 - cp's OEIS frontend

A189912 Extended Motzkin numbers, Sum_{k>=0} C(n,k)*C(k), where C(k) is the extended Catalan number A057977(k).

1, 2, 4, 10, 25, 66, 177, 484, 1339, 3742, 10538, 29866, 85087, 243478, 699324, 2015082, 5822619, 16865718, 48958404, 142390542, 414837699, 1210439958, 3536809521, 10347314544, 30306977757, 88861597426, 260798283502, 766092871654, 2252240916665

Offset: 0

Peter Luschny, May 01 2011

nonn

a(n) = Sum_{k=0..n} binomial(n,k)*A057977(k). For comparison:
A001006(n) = Sum_{k=0..n} binomial(n,k)*A057977(k)*[k is even],
A005717(n) = Sum_{k=0..n} binomial(n,k)*A057977(k)*[k is odd].
Thus one might simply say: The extended Motzkin numbers are the binomial sum of the extended Catalan numbers. Moreover: The Catalan numbers aerated with 0's at odd positions (A126120) are the inverse binomial transform of the Motzkin numbers (A001006). The complementary Catalan numbers (A001700) aerated with 0's at even positions (A138364) are the inverse binomial transform of the complementary Motzkin numbers (A005717). The extended Catalan numbers (A057977 = A126120 + A138364) are the inverse binomial transform of the extended Motzkin numbers (A189912).
David Scambler observed that [1, a(n-1)] for n >= 1 count the Dyck paths of semilength n which satisfy the condition "number of peaks <= number of returns + number of hills". - Peter Luschny, Oct 22 2012

G. C. Greubel, Table of n, a(n) for n = 0..1000
Per Alexandersson, Proof of Werner Schulte's formula.
A. Asinowski and G. Rote, Point sets with many non-crossing matchings, arXiv preprint arXiv:1502.04925 [cs.CG], 2015.
Peter Luschny, Die schwingende Fakultät und Orbitalsysteme, August 2011.
Peter Luschny, The Scambler_statistic_on_Dyck_words.

Cf. A001006, A001700, A005717, A057977, A126120, A138364, A217539, A217540.

A189912 := proc(n) local k;
add(n!/(((n-k)!*iquo(k,2)!^2)*(iquo(k,2)+1)),k=0..n) end:
M := proc(n) option remember; `if`(n<2, 1, (3*(n-1)*M(n-2)+(2*n+1)*M(n-1))/(n+2)) end:
A189912 := n -> n*M(n-1)+M(n);
seq(A189912(i), i=0..28); # Peter Luschny, Sep 12 2011

A057977[n_] := n!/(Quotient[n, 2]!^2*(Quotient[n, 2] + 1)); a[n_] := Sum[Binomial[n, k]*A057977[k], {k, 0, n}]; Table[a[n], {n, 0, 28}] (* Jean-François Alcover, May 21 2013, after Peter Luschny *)
Table[Sum[n!/(((n-k)!*Floor[k/2]!^2)*(Floor[k/2]+1)), {k,0,n}], {n,0,30}] (* G. C. Greubel, Jan 24 2017 *)
A057977[n_] :=  Sum[n! (n + 1 - 2 k)/((k + 1)! (k!) (n - 2 k)!), {k, 0, n}] (* Per W. Alexandersson, May 28 2020 *)

a(n) = sum(k=0, n, binomial(n,k)*k!/( (k\2)!^2 * (k\2+1)) );
vector(30, n, a(n-1)) \\ G. C. Greubel, Jan 24 2017; Mar 28 2020

@CachedFunction
def M(n): return (3*(n-1)*M(n-2)+(2*n+1)*M(n-1))/(n+2) if n>1 else 1
A189912 = lambda n: n*M(n-1) + M(n)
[A189912(i) for i in (0..28)] # Peter Luschny, Oct 22 2012

a(n) = Sum_{k=0..n} n!/(((n-k)!*floor(k/2)!^2)*(floor(k/2)+1)).
Recurrence: (n+2)*(n^2 + 2*n - 5)*a(n) = (2*n^3 + 7*n^2 - 14*n - 7)*a(n-1) + 3*(n-1)*(n^2 + 4*n - 2)*a(n-2). - Vaclav Kotesovec, Mar 20 2014
a(n) ~ 3^(n+1/2) / (2*sqrt(Pi*n)). - Vaclav Kotesovec, Mar 20 2014
Conjecture: a(n) = Sum_{k=0..floor(n/2)} (n+1-2*k)*A055151(n,k). - Werner Schulte, Oct 23 2016
a(n) = Sum_{k=0..floor(n/2)} (n+1-2*k)*n!/(k!*(k+1)!*(n-2*k)!). - Per W. Alexandersson, May 28 2020

A274886 Triangle read by rows, the q-analog of the extended Catalan numbers A057977.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 2, 2, 2, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 2, 3, 4, 4, 5, 4, 4, 3, 2, 1, 1, 1, 0, 1, 1, 2, 1, 2, 1, 2, 1, 1, 0, 1, 1, 1, 2, 3, 5, 6, 8, 9, 11, 11, 12, 11, 11, 9, 8, 6, 5, 3, 2, 1, 1, 1, 0, 1, 1, 2, 2, 3, 2, 4, 3, 4, 3, 4, 2, 3, 2, 2, 1, 1, 0, 1

Offset: 0

Peter Luschny, Jul 20 2016

The q-analog of the extended Catalan numbers A057977 are univariate polynomials over the integers with degree floor((n+1)/2)*(floor((n+1)/2)-1)+1.
The q-analog of the Catalan numbers are A129175.
For a combinatorial interpretation in terms of the major index statistic of orbitals see A274888 and the link 'Orbitals'.

			The polynomials start:
[0] 1
[1] 1
[2] 1
[3] q^2 + q + 1
[4] q^2 + 1
[5] (q^2 + 1) * (q^4 + q^3 + q^2 + q + 1)
[6] (q^2 - q + 1) * (q^4 + q^3 + q^2 + q + 1)
The coefficients of the polynomials are:
[ 0] [1]
[ 1] [1]
[ 2] [1]
[ 3] [1, 1, 1]
[ 4] [1, 0, 1]
[ 5] [1, 1, 2, 2, 2, 1, 1]
[ 6] [1, 0, 1, 1, 1, 0, 1]
[ 7] [1, 1, 2, 3, 4, 4, 5, 4, 4, 3, 2, 1, 1]
[ 8] [1, 0, 1, 1, 2, 1, 2, 1, 2, 1, 1, 0, 1]
[ 9] [1, 1, 2, 3, 5, 6, 8, 9, 11, 11, 12, 11, 11, 9, 8, 6, 5, 3, 2, 1, 1]
[10] [1, 0, 1, 1, 2, 2, 3, 2, 4, 3, 4, 3, 4, 2, 3, 2, 2, 1, 1, 0, 1]

Peter Luschny, Orbitals

Cf. A057977, A129175, A274885, A274888.

QExtCatalan := proc(n) local h, p, P;
P := x -> QDifferenceEquations:-QPochhammer(q,q,x);
h := iquo(n, 2): p := `if`(n::even, 1-q, 1); (p*P(n))/(P(h)*P(h+1));
expand(simplify(expand(%))); seq(coeff(%, q, j), j=0..degree(%)) end:
seq(QExtCatalan(n, q), n=0..10);

(* Function QBinom1 is defined in A274885. *)
QExtCatalan[n_] := QBinom1[n] / QBinomial[n+1,1,q]; Table[CoefficientList[ QExtCatalan[n] // FunctionExpand,q], {n,0,10}] // Flatten

# uses[q_binom1 from A274885]
from sage.combinat.q_analogues import q_int
def q_ext_catalan_number(n): return q_binom1(n)//q_int(n+1)
for n in (0..10): print([n], q_ext_catalan_number(n).list())

# uses[unit_orbitals from A274709]
# Brute force counting
def catalan_major_index(n):
    S = [0]*(((n+1)//2)^2 + ((n+1) % 2) - (n//2))
    for u in unit_orbitals(n):
        if any(x > 0 for x in accumulate(u)): continue # never rise above 0
        L = [i+1 if u[i+1] < u[i] else 0 for i in (0..n-2)]
        #    i+1 because u is 0-based whereas convention assumes 1-base.
        S[sum(L)] += 1
    return S
for n in (0..10): print(catalan_major_index(n))

q-extCatalan(n,q) = (p*P(n,q))/(P(h,q)*P(h+1,q)) with P(n,q) = q-Pochhammer(n,q), h = floor(n/2) and p = 1-q if n is even else 1.

A080388 Erroneous version of A057977.

Original entry on oeis.org

1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 6, 1, 2, 3, 1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 4, 1, 30, 1, 1, 3, 2, 5, 6, 1, 2, 3, 10, 1, 6, 1, 4, 15, 2, 1, 6, 1, 2, 3, 4, 1, 2, 1, 28, 1, 2, 1, 4, 1, 2, 7, 1, 1, 6, 1, 2, 3, 14, 1, 2, 1, 2, 1, 4, 7, 2, 1, 10, 1, 2, 1, 84, 5, 2, 3, 4, 1, 90, 7, 4, 3, 2, 5, 6, 1, 2, 9, 4, 1, 6

Offset: 1

dead

A239453 Convolution of the generalized Catalan numbers A057977 with themselves.

Original entry on oeis.org

1, 2, 3, 8, 11, 30, 43, 112, 172, 420, 694, 1584, 2809, 6006, 11379, 22880, 46088, 87516, 186562, 335920, 754646, 1293292, 3050238, 4992288, 12319816, 19315400, 49725004, 74884320, 200571541, 290845350, 808559299, 1131445440, 3257808976, 4407922860, 13119940234

Offset: 0

Peter Luschny, Mar 19 2014

nonn

Cf. A162551.

def A239453_list(n):
    r = sqrt(1-4*x^2)
    g = lambda x: (1-r)*(r+x)/(2*x^2*r)
    s = taylor(g(x), x, 0, n+1)
    f = [s.coefficient(x, j) for j in (0..n+1)]
    return [add(f[k]*f[j-k] for k in (0..j)) for j in (0..n)]
A239453_list(36)

D-finite with recurrence -(n+4)*(137*n-1035)*a(n) +(383*n^2-1622*n-5421)*a(n-1) +4*(274*n^2-1385*n-3534)*a(n-2) +4*(-766*n^2+4393*n+555)*a(n-3) +16*(-137*n^2+898*n-606)*a(n-4) +16*(n-3)*(383*n-1622)*a(n-5)=0. - R. J. Mathar, Feb 03 2025

A274883 Triangle read by rows, T(n,k) = 2^kbinomial(n,k)A057977(n-k) for n>=0 and 0<=k<=n.

Original entry on oeis.org

1, 1, 2, 1, 4, 4, 3, 6, 12, 8, 2, 24, 24, 32, 16, 10, 20, 120, 80, 80, 32, 5, 120, 120, 480, 240, 192, 64, 35, 70, 840, 560, 1680, 672, 448, 128, 14, 560, 560, 4480, 2240, 5376, 1792, 1024, 256, 126, 252, 5040, 3360, 20160, 8064, 16128, 4608, 2304, 512

Offset: 0

Peter Luschny, Jul 14 2016

			Triangle starts:
                       1;
                      1, 2;
                    1, 4, 4;
                  3, 6, 12, 8;
               2, 24, 24, 32, 16;
            10, 20, 120, 80, 80, 32;
         5, 120, 120, 480, 240, 192, 64;
     35, 70, 840, 560, 1680, 672, 448, 128;
14, 560, 560, 4480, 2240, 5376, 1792, 1024, 256;

Cf. A000079 (T(n,n)), A057977 (T(n,0)), A077587 (row sum).

Cf. A189912. Row reversed A091894 is a subtriangle.

T := (n,k) -> 2^k*binomial(n,k)*((n-k)!/floor((n-k)/2)!^2)/(floor((n-k)/2)+1);
seq(seq(T(n,k), k=0..n), n=0..9);

A138364 The number of Motzkin n-paths with exactly one flat step.

Original entry on oeis.org

0, 1, 0, 3, 0, 10, 0, 35, 0, 126, 0, 462, 0, 1716, 0, 6435, 0, 24310, 0, 92378, 0, 352716, 0, 1352078, 0, 5200300, 0, 20058300, 0, 77558760, 0, 300540195, 0, 1166803110, 0, 4537567650, 0, 17672631900, 0, 68923264410, 0, 269128937220, 0

Offset: 0

Andrew V. Sutherland, Mar 16 2008

An aerated version of A001700, which is the main entry for this sequence.

Number of paths in the half-plane x>=0, from (0,0) to (n,1), and consisting of steps U=(1,1) and D=(1,-1). For example, for n=3, we have the 3 paths: UUD, UDU, DUU. - José Luis Ramírez Ramírez, Apr 19 2015

			a(5)=10 since the coefficient of z^5 in I_1(2z) is binomial(5,3)=10.

Jerome Spanier and Keith B. Oldham, "Atlas of Functions", Ch. 49, Hemisphere Publishing Corp., 1999.

G. C. Greubel, Table of n, a(n) for the first 50 rows, flattened
Kiran S. Kedlaya and Andrew V. Sutherland, Hyperelliptic Curves, L-Polynomials, and Random Matrices. In: Arithmetic, Geometry, Cryptography, and Coding Theory: International Conference, November 5-9, 2007, CIRM, Marseilles, France. (Contemporary Mathematics; v.487)

Cf. A001700, A057977, A126869.

&cat[[0, Binomial(n, (n+1) div 2)]: n in [1..50 by 2]]; // Vincenzo Librandi, Apr 20 2015

a[ n_] := SeriesCoefficient[ n! BesselI[ 1, 2 x], {x, 0, n}]; (* Michael Somos, Mar 19 2014 *)

x='x+O('x^66); concat([0], Vec( -(sqrt(1-4*x^2)+2*x^2-1) / (x*sqrt(1-4*x^2)+4*x^3-x))) \\ Joerg Arndt, May 08 2013

from math import comb
def A138364(n): return comb(n,n>>1) if n&1 else 0 # Chai Wah Wu, Aug 25 2025

def A138364(n):
    if is_even(n): return 0
    return binomial(n,n//2)
[A138364(n) for n in (0..42)]  # Peter Luschny, Mar 18 2014

a(n) = binomial(n,(n+1)/2) for n odd, 0 otherwise.
E.g.f.: I_1(2z), where I_1 is the hyperbolic Bessel function of order 1.
a(n) = (1/(2*Pi))*integral(x=-2..2, x^n*x/sqrt((2+x)*(2-x))). - Peter Luschny, Sep 12 2011
G.f.: -(sqrt(1-4*x^2)+2*x^2-1)/(x*sqrt(1-4*x^2)+4*x^3-x). - Vladimir Kruchinin, Mar 08 2013
a(n) + A126120(n) = A057977(n). - Peter Luschny, Mar 18 2014
G.f.: z*C(z^2)/(1-2*z^2*C(z^2)), where C(z) is the g.f. of Catalan numbers. - José Luis Ramírez Ramírez, Apr 19 2015
a(n) = Integral_[-Pi,Pi] cos^(n+1)/(2^(n-1)*Pi). - M. F. Hasler, Jul 12 2018

New name is a comment by David Scambler, May 02 2013. - Peter Luschny, Mar 18 2014

A232500 Oscillating orbitals over n sectors (nonpositive values indicating there exist none).

Original entry on oeis.org

-1, -1, 0, 0, 2, 10, 10, 70, 42, 378, 168, 1848, 660, 8580, 2574, 38610, 10010, 170170, 38896, 739024, 151164, 3174444, 587860, 13520780, 2288132, 57203300, 8914800, 240699600, 34767720, 1008263880, 135727830, 4207562730, 530365050, 17502046650, 2074316640

Offset: 0

Peter Luschny, Jan 05 2014

A planar orbital system is a family of concentric circles in a plane divided into n sectors. An orbital is a closed path consisting of arcs on these circles such that at each boundary of a sector the path jumps to the next inner or outer circle. One exception is allowed: if n is odd the path might continue on the same circle, but just once. After fixing one circle as the central circle there are three types of orbitals: a high orbital is always above the central circle, a low orbital is always below the central circle, and an oscillating orbital which is neither a high nor a low orbital. The number of all orbitals is A056040(n), the number of high orbitals, which is the same as the number of low orbitals, is A057977(n), and the number of oscillating orbitals is this a(n) (for n >= 4).

Peter Luschny, Illustrating swinging orbitals.

Cf. A056040, A057977.

f := (z/(1-4*z^2)-3-1/z+1/z^2)/sqrt(1-4*z^2)-1/z^2+1/z;
seq(coeff(series(f, z, n+2), z, n), n=0..19);
g := (1+x)*BesselI(0, 2*x)-2*(1+1/x)*BesselI(1, 2*x);
seq(n!*coeff(series(g,x,n+2),x,n), n=0..19);

sf[n_] := n!/Quotient[n, 2]!^2; a[n_] := sf[n]*(1-2/(Quotient[n, 2]+1)); Table[a[n], {n, 0, 40}] (* Jean-François Alcover, Feb 11 2015 *)
nxt[{n_,a_}]:={n+1,If[EvenQ[n],a(n+1),a (4(n-1))/((n-3)(n+3))]}; Join[{-1,-1,0,0,2},NestList[nxt,{5,10},40][[;;,2]]] (* Harvey P. Dale, Dec 16 2024 *)

a(n) = n!/(n\2)!^2*(n\2-1)/(n\2+1) \\ Charles R Greathouse IV, Jul 30 2016

def A232500():
    r, n = 1, 0
    while True:
        yield r*(n//2-1)/(n//2+1)
        n += 1
        r *= 4/n if is_even(n) else n
a = A232500(); [next(a) for i in range(36)]

O.g.f.: (z/(1-4*z^2) - 3 - 1/z + 1/z^2)/sqrt(1-4*z^2) - 1/z^2 + 1/z.
E.g.f.: (1+x)*BesselI(0, 2*x)-2*(1+1/x)*BesselI(1, 2*x).
a(n) = (n!/k!^2)*(k-1)/(k+1) where k = floor(n/2).
Recurrence: If n > 4 then a(n) = a(n-1)*n if n is odd else a(n-1)*4*(n-2)/((n-4)*(n+2)).
a(n) = A056040(n) * (1 - 2/(floor(n/2) + 1)).
a(n) = A056040(n) - 2*A057977(n).
Asymptotic: log(a(n)) ~ (n*log(4) - log(Pi) - (-1)^n*(log(n/2) + 1/(2*n)))/2 + log(1 - 8/(2*n + 3 + (-1)^n)) for n >= 4.
D-finite with recurrence: +(n+2)*a(n) -n*a(n-1) +(-11*n+2)*a(n-2) +(9*n-16)*a(n-3) +20*(2*n-5)*a(n-4) +20*(-n+3)*a(n-5) +48*(-n+5)*a(n-6)=0. - R. J. Mathar, Feb 21 2020

A241477 Triangle read by rows, number of orbitals classified with respect to the first zero crossing, n>=1, 1<=k<=n.

Original entry on oeis.org

1, 0, 2, 2, 2, 2, 0, 4, 0, 2, 6, 12, 4, 2, 6, 0, 12, 0, 4, 0, 4, 20, 60, 12, 12, 12, 4, 20, 0, 40, 0, 12, 0, 8, 0, 10, 70, 280, 40, 60, 36, 24, 40, 10, 70, 0, 140, 0, 40, 0, 24, 0, 20, 0, 28, 252, 1260, 140, 280, 120, 120, 120, 60, 140, 28, 252, 0, 504, 0

Offset: 1

Peter Luschny, Apr 23 2014

For the combinatorial definitions see A232500. An orbital w over n sectors has its first zero crossing at k if k is the smallest j such that the partial sum(1<=i<=j, w(i))) = 0, where w(i) are the jumps of the orbital represented by -1, 0, 1.

			[1], [ 1]
[2], [ 0,  2]
[3], [ 2,  2,  2]
[4], [ 0,  4,  0,  2]
[5], [ 6, 12,  4,  2,  6]
[6], [ 0, 12,  0,  4,  0, 4]
[7], [20, 60, 12, 12, 12, 4, 20]

Row sums: A056040.

Cf. A232500.

A241477 := proc(n, k)
  if n = 0 then 1
elif k = 0 then 0
elif irem(n, 2) = 0 and irem(k, 2) = 1 then 0
elif k = 1 then (n-1)!/iquo(n-1,2)!^2
else 2*(n-k)!*(k-2)!/iquo(k,2)/(iquo(k-2,2)!*iquo(n-k,2)!)^2
  fi end:
for n from 1 to 9 do seq(A241477(n, k), k=1..n) od;

T[n_, k_] := Which[n == 0, 1, k == 0, 0, Mod[n, 2] == 0 && Mod[k, 2] == 1,  0, k == 1, (n-1)!/Quotient[n-1, 2]!^2, True, 2*(n-k)!*(k-2)!/Quotient[k, 2]/(Quotient[k-2, 2]!*Quotient[n-k, 2]!)^2];
Table[T[n, k], {n, 1, 12}, {k, 1, n}] // Flatten (* Jean-François Alcover, Jun 20 2018, from Maple *)

def A241477_row(n):
    if n == 0: return [1]
    Z = [0]*n; T = [0] if is_odd(n) else []
    for i in (1..n//2): T.append(-1); T.append(1)
    for p in Permutations(T):
        i = 0; s = p[0]
        while s != 0: i += 1; s += p[i];
        Z[i] += 1
    return Z
for n in (1..9): A241477_row(n)

If n is even and k is odd then T(n, k) = 0 else if k = 1 then T(n, 1) = A056040(n-1) else T(n, k) = 2*A057977(k-2)*A056040(n-k).
T(n, n) = A241543(n).
T(n+1, 1) = A126869(n).
T(2*n, 2*n) = |A002420(n)|.
T(2*n+1, 1) = A000984(n).
T(2*n+1, n+1) = A241530(n).
T(2*n+2, 2) = A028329(n).
T(4*n, 2*n) = |A010370(n)|.
T(4*n, 4*n) = |A024491(n)|.
T(4*n+1, 1) = A001448(n).
T(4*n+1, 2*n+1) = A002894(n).

A274709 A statistic on orbital systems over n sectors: the number of orbitals which rise to maximum height k over the central circle.

Original entry on oeis.org

1, 1, 1, 1, 3, 3, 2, 3, 1, 10, 15, 5, 5, 9, 5, 1, 35, 63, 35, 7, 14, 28, 20, 7, 1, 126, 252, 180, 63, 9, 42, 90, 75, 35, 9, 1, 462, 990, 825, 385, 99, 11, 132, 297, 275, 154, 54, 11, 1, 1716, 3861, 3575, 2002, 702, 143, 13, 429, 1001, 1001, 637, 273, 77, 13, 1

Offset: 0

Peter Luschny, Jul 09 2016

The definition of an orbital system is given in A232500 (see also the illustration there). The number of orbitals over n sectors is counted by the swinging factorial A056040.
Note that (sum row_n) / row_n(0) = 1,1,2,2,3,3,4,4,..., i.e. the swinging factorials are multiples of the extended Catalan numbers A057977 generalizing the fact that the central binomials are multiples of the Catalan numbers.
T(n, k) is a subtriangle of the extended Catalan triangle A189231.

			Triangle read by rows, n>=0. The length of row n is floor((n+2)/2).
[ n] [k=0,1,2,...] [row sum]
[ 0] [  1] 1
[ 1] [  1] 1
[ 2] [  1,   1] 2
[ 3] [  3,   3] 6
[ 4] [  2,   3,   1] 6
[ 5] [ 10,  15,   5] 30
[ 6] [  5,   9,   5,   1] 20
[ 7] [ 35,  63,  35,   7] 140
[ 8] [ 14,  28,  20,   7,  1] 70
[ 9] [126, 252, 180,  63,  9] 630
[10] [ 42,  90,  75,  35,  9,  1] 252
[11] [462, 990, 825, 385, 99, 11] 2772
[12] [132, 297, 275, 154, 54, 11, 1] 924
T(6, 2) = 5 because the five orbitals [-1, 1, 1, 1, -1, -1], [1, -1, 1, 1, -1, -1], [1, 1, -1, -1, -1, 1], [1, 1, -1, -1, 1, -1], [1, 1, -1, 1, -1, -1] raise to maximal height of 2 over the central circle.

Peter Luschny, The lost Catalan numbers
Peter Luschny, Orbitals

Cf. A008313, A039599 (even rows), A047072, A056040 (row sums), A057977 (col 0), A063549 (col 0), A112467, A120730, A189230 (odd rows aerated), A189231, A232500.

Other orbital statistics: A241477 (first zero crossing), A274706 (absolute integral), A274708 (number of peaks), A274710 (number of turns), A274878 (span), A274879 (returns), A274880 (restarts), A274881 (ascent).

S := proc(n,k) option remember; `if`(k>n or k<0, 0, `if`(n=k, 1, S(n-1,k-1)+
modp(n-k,2)*S(n-1,k)+S(n-1,k+1))) end: T := (n,k) -> S(n,2*k);
seq(print(seq(T(n,k), k=0..iquo(n,2))), n=0..12);

from itertools import accumulate
# Brute force counting
def unit_orbitals(n):
    sym_range = [i for i in range(-n+1, n, 2)]
    for c in Combinations(sym_range, n):
        P = Permutations([sgn(v) for v in c])
        for p in P: yield p
def max_orbitals(n):
    if n == 0: return [1]
    S = [0]*((n+2)//2)
    for u in unit_orbitals(n):
        L = list(accumulate(u))
        S[max(L)] += 1
    return S
for n in (0..10): print(max_orbitals(n))

A080383 Number of j (0 <= j <= n) such that the central binomial coefficient C(n,floor(n/2)) = A001405(n) is divisible by C(n,j).

Original entry on oeis.org

1, 2, 3, 4, 3, 6, 3, 6, 3, 6, 3, 6, 7, 10, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 8, 3, 6, 3, 6, 7, 10, 3, 6, 3, 6, 3, 8, 3, 6, 5, 10, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 7, 10, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6, 7, 10, 3, 6, 3, 6, 7, 10, 3, 6, 3, 6, 3, 6, 3, 6, 3, 6

Offset: 0

Labos Elemer, Mar 12 2003

nonn

			For n <= 500 only a few values of a(n) arise: {1,2,3,4,5,6,7,8,10,11,14}.
From _Jon E. Schoenfield_, Sep 15 2019: (Start)
a(n)=1 occurs only at n=0.
a(n)=2 occurs only at n=1.
a(n)=3 occurs for all even n > 0 such that C(n,j) divides C(n,n/2) only at j = 0, n/2, and n. (This is the case for about 4/9 of the first 100000 terms, and there appear to be nearly as many terms for which a(n)=6.)
a(n)=4 occurs only at n=3.
For n <= 100000, the only values of a(n) that occur are 1..16, 18, 19, 22, 23, and 26.
   k | Indices n (up to 100000) at which a(n)=k
  ---+-------------------------------------------------------
   1 | 0
   2 | 1
   3 | 2, 4, 6, 8, 10, 14, 16, 18, 20, 22, 24, ...
   4 | 3
   5 | 40, 176, 208, 480, 736, 928, 1248, 1440, ... (A327430)
   6 | 5, 7, 9, 11, 15, 17, 19, 21, 23, 27, 29, ... (A080384)
   7 | 12, 30, 56, 84, 90, 132, 154, 182, 220, ...  (A080385)
   8 | 25, 37, 169, 199, 201, 241, 397, 433, ...    (A080386)
   9 | 1122, 1218, 5762, 11330, 12322, 15132, ...   (A327431)
  10 | 13, 31, 41, 57, 85, 91, 133, 155, 177, ...   (A080387)
  11 | 420, 920, 1892, 1978, 2444, 2914, 3198, ...
  12 | 1103, 1703, 2863, 7773, 10603, 15133, ...
  13 | 12324, 37444
  14 | 421, 921, 1123, 1893, 1979, 1981, 2445, ...
  15 | 4960, 6956, 13160, 16354, 18542, 24388, ...
  16 | 11289, 16483, 36657, 62653, 89183
  17 |
  18 | 4961, 6957, 12325, 13161, 16355, 18543, ...
  19 | 16356, 88510, 92004
  20 |
  21 |
  22 | 16357, 88511, 90305, 92005
  23 | 90306
  24 |
  25 |
  26 | 90307
(End)

Vaclav Kotesovec, Table of n, a(n) for n = 0..100000 (first 1000 terms from Vincenzo Librandi, terms 1001..9999 from David A. Corneth)

Cf. A001405, A000225, A057977, A022292, A020475, A067348, A042996.
Cf. A327430, A080384, A080385, A080386, A327431, A080387.
Cf. A080393.

[#[j:j in [0..n]| Binomial(n,Floor(n/2)) mod Binomial(n,j) eq 0]:n in [0..100]]; // Marius A. Burtea, Sep 15 2019

Table[Count[Table[IntegerQ[Binomial[n, Floor[n/2]]/Binomial[n, j]], {j, 0, n}], True], {n, 0, 500}] (* adapted by Vincenzo Librandi, Jul 29 2017 *)

a(n) = my(b=binomial(n, n\2)); sum(i=0, n, (b % binomial(n, i)) == 0); \\ Michel Marcus, Jul 29 2017

a(n) = {if(n==0, return(1)); my(bb = binomial(n, n\2), b = n); res = 2 + !(n%2) + 2 * (n>2 && n%2 == 1); for(i = 2, (n-1)\2, res += 2*(bb%b==0); b *= (n + 1 - i) / i); res} \\ David A. Corneth, Jul 29 2017

Edited by Dean Hickerson, Mar 14 2003

Offset corrected by David A. Corneth, Jul 29 2017

cp's OEIS Frontend

A189912 Extended Motzkin numbers, Sum_{k>=0} C(n,k)*C(k), where C(k) is the extended Catalan number A057977(k).

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A274886 Triangle read by rows, the q-analog of the extended Catalan numbers A057977.

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A080388 Erroneous version of A057977.

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A239453 Convolution of the generalized Catalan numbers A057977 with themselves.

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A274883 Triangle read by rows, T(n,k) = 2^k*binomial(n,k)*A057977(n-k) for n>=0 and 0<=k<=n.

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A138364 The number of Motzkin n-paths with exactly one flat step.

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A232500 Oscillating orbitals over n sectors (nonpositive values indicating there exist none).

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A241477 Triangle read by rows, number of orbitals classified with respect to the first zero crossing, n>=1, 1<=k<=n.

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A274883 Triangle read by rows, T(n,k) = 2^kbinomial(n,k)A057977(n-k) for n>=0 and 0<=k<=n.