

A046802


Triangle of hvectors of the stellahedra. Enumerates positroid cells of the totally nonnegative Grassmanian G+(k,n).


23



1, 1, 1, 1, 3, 1, 1, 7, 7, 1, 1, 15, 33, 15, 1, 1, 31, 131, 131, 31, 1, 1, 63, 473, 883, 473, 63, 1, 1, 127, 1611, 5111, 5111, 1611, 127, 1, 1, 255, 5281, 26799, 44929, 26799, 5281, 255, 1, 1, 511, 16867, 131275, 344551, 344551, 131275, 16867, 511, 1, 1, 1023, 52905
(list;
table;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,5


COMMENTS

Row sums give A000522.  Roger L. Bagula, Nov 21 2009
With offset=0, T(n,k) is the number of positroid cells of the totally nonnegative Grassmannian G+(k,n) (cf. Postnikov/Williams).  Tom Copeland, Oct 10 2014
See A248727 for a simple transformation of the row polynomials of this entry that produces the umbral compositional inverses of the polynomials of A074909, related to the face polynomials of the simplices.  Tom Copeland, Jan 21 2015
From Tom Copeland, Jan 24 2015: (Start)
The reciprocal of this entry's e.g.f. is [t e^(xt)  e^(x)] / (t1) = 1  (1+t) x + (1+t+t^2) x^2/2!  (1+t+t^2+t^3) x^3/3! + ... = e^(q.(0;t)x), giving the base sequence (q.(0;t))^n = q_n(0;t) = (1)^n [1t^(n+1)] / (1t) for the umbral compositional inverses (q.(0;t)+z)^n = q_n(z;t) of the Appell polynomials associated with this entry, p_n(z;t) below, i.e., q_n(p.(z;t)) = z^n = p_n(q.(z;t)), in umbral notation. The relations in A133314 then apply between the two sets of base polynomials. (Inserted missing index in a formula  Mar 03 2016.)
The associated o.g.f. for the umbral inverses is Og(x) = x / (1x q.(0:t)) = x / [(1+x)(1+tx)] = x / [1+(1+t)x+tx^2]. Applying A134264 to h(x) = x / Og(x) = 1 + (1+t) x + t x^2 leads to an o.g.f. for the Narayana polynomials A001263 as the comp. inverse Oginv(x) = [1(1+t)xsqrt[12(1+t)x+((t1)x)^2]] / (2xt). Note that Og(x) gives the signed hpolynomials of the simplices and that Oginv(x) gives the hpolynomials of the simplicial duals of the Stasheff polynomials, or type A associahedra. Contrast this with A248727 = A046802 * A007318, which has o.g.f.s related to the corresponding fpolynomials. (End)
The Appell polynomials p_n(x;t) in the formulas below specialize to the Swissknife polynomials of A119879 for t = 1, so the Springer numbers A001586 are given by 2^n p_n(1/2;1).  Tom Copeland, Oct 14 2015
The row polynomials are the hpolynomials associated to the stellahedra, whose fpolynomials are the row polynomials of A248727. Cf. page 60 of the Buchstaber and Panov link.  Tom Copeland, Nov 08 2016
From p. 60 of the Buchstaber and Panov link, S = P * C / T where S, P, C, and T are the bivariate e.g.f.s of the h vectors of the stellahedra, permutahedra, hypercubes, and (n1)simplices, respectively.  Tom Copeland, Jan 09 2017


REFERENCES

L. Comtet, Advanced Combinatorics, Reidel, Holland, 1974, page 245 [From Roger L. Bagula, Nov 21 2009]
D. Singh, The numbers L(m,n) and their relations with prepared Bernoulli and Eulerian numbers, Math. Student, 20 (1952), 6670.


LINKS

Table of n, a(n) for n=1..58.
P. Barry, General Eulerian Polynomials as Moments Using Exponential Riordan Arrays, Journal of Integer Sequences, 16 (2013), #13.9.6.
Paul Barry, Three Études on a sequence transformation pipeline, arXiv:1803.06408 [math.CO], 2018.
Carolina Benedetti, Anastasia Chavez, Daniel Tamayo, Quotients of uniform positroids, arXiv:1912.06873 [math.CO], 2019.
V. Buchstaber and T. Panov Toric Topology, arXiv:1210.2368v3 [math.AT], 2014.
Jan Geuenich, Tilting modules for the Auslander algebra of K[x]/(xn), arXiv:1803.10707 [math.RT], 2018.
A. Postnikov, Total positivity, Grassmannians, and networks, arXiv:math/0609764 [math.CO], 2006.
D. Singh, The numbers L(m,n) and their relations with prepared Bernoulli and Eulerian numbers, Math. Student, 20 (1952), 6670. [Annotated scanned copy]
L. K. Williams, Enumeration of totally positive Grassmann cells, arXiv:math/0307271 [math.CO], 20032004.
L. Williams, The Positive Grassmannian (from a mathematician's perspective), 2014


FORMULA

a(m, n) = Sum_{r = n1..m1} C(m1, r)*L(r, n1), L = A123125 (Eulerian numbers).
E.g.f.: (y1)*exp(x*y)/(yexp((y1)*x)).  Vladeta Jovovic, Sep 20 2003
p(t,x) = (1  x)*exp(t)/(1  x*exp(t*(1  x))).  Roger L. Bagula, Nov 21 2009
With offset=0, T(n,0)=1 otherwise T(n,k) = sum_{i=0..k1} C(n,i)((ik)^i*(ki+1)^(ni)  (ik+1)^i*(ki)^(ni)) (cf. Williams).  Tom Copeland, Oct 10 2014
With offset 0, T = A007318 * A123125. Second column is A000225; 3rd, appears to be A066810.  Tom Copeland, Jan 23 2015
A raising operator (with D = d/dx) associated with this entry's row polynomials is R = x + t + (1t) / [1t e^{(1t)D}] = x + t + 1 + t D + (t+t^2) D^2/2! + (t+4t^2+t^3) D^3/3! + ... , containing the e.g.f. for the Eulerian polynomials of A123125. Then R^n 1 = (p.(0;t)+x)^n = p_n(x;t) are the Appell polynomials with this entry's row polynomials p_n(0;t) as the base sequence. Examples of this formalism are given in A028246 and A248727.  Tom Copeland, Jan 24 2015
With offset 0, T = A007318*(padded A090582)*(inverse of A097805) = A007318*(padded A090582)*(padded A130595) = A007318*A123125 = A007318*(padded A090582)*A007318*A097808*A130595, where padded matrices are of the form of padded A007318, which is A097805. Inverses of padded matrices are just the padded versions of inverses of the unpadded matrices. This relates the face vectors, or fvectors, and hvectors of the permutahedra / permutohedra to those of the stellahedra / stellohedra.  Tom Copeland, Nov 13 2016
Umbrally, the row polynomials (offset 0) are r_n(x) = (1 + q.(x))^n, where (q.(x))^k = q_k(x) are the row polynomials of A123125.  Tom Copeland, Nov 16 2016
From the previous umbral statement, OP(x,d/dy) y^n = (y + q.(x))^n, where OP(x,y) = exp[y * q.(x)] = (1x)/(1x*exp((1x)y)), the e.g.f. of A123125, so OP(x,d/dy) y^n evaluated at y = 1 is r_n(x), the nth row polynomial of this entry, with offset 0.  Tom Copeland, Jun 25 2018
Consolidating some formulas in this entry and A248727, in umbral notation for concision, with all offsets 0: Let A_n(x;y) = (y + E.(x))^n, an Appell sequence in y where E.(x)^k = E_k(x) are the Eulerian polynomials of A123125. Then the row polynomials of this entry (A046802, the hpolynomials of the stellahedra) are given by h_n(x) = A_n(x;1); the row polynomials of A248727 (the face polynomials of the stellahedra), by f_n(x) = A_n(1 + x;1); the Swissknife polynomials of A119879, by Sw_n(x) = A_n(1;1 + x); and the row polynomials of the Worpitsky triangle (A130850), by w_n(x) = A(1 + x;0). Other specializations of A_n(x;y) give A090582 (the fpolynomials of the permutohedra, cf. also A019538) and A028246 (another version of the Worpitsky triangle).  Tom Copeland, Jan 24 2020


EXAMPLE

The triangle a(m, n) begins:
m\n 1 2 3 4 5 6 7 8
1: 1
2: 1 1
3: 1 3 1
4: 1 7 7 1
5: 1 15 33 15 1
6: 1 31 131 131 31 1
7: 1 63 473 883 473 63 1
8: 1 127 1611 5111 5111 1611 127 1
... Reformatted.  Wolfdieter Lang, Feb 14 2015


MAPLE

T := (n, k) > add(binomial(n1, r)*combinat:eulerian1(r, rk+1), r = k1 .. n1):
for n from 1 to 8 do seq(T(n, k), k=1..n) od; # Peter Luschny, Jun 27 2018


MATHEMATICA

p[t_] = (1  x)*Exp[t]/(1  x*Exp[t*(1  x)])
Flatten[ Table[ CoefficientList[FullSimplify[ExpandAll[ n!*SeriesCoefficient[ Series[p[t], {t, 0, 30}], n]]], x], {n, 0, 10}]] (* Roger L. Bagula, Nov 21 2009 *)
t[_, 1] = 1; t[n_, n_] = 1; t[n_, 2] = 2^(n1)1; t[n_, k_] = Sum[((ik+1)^i*(ki)^(ni1)  (ik+2)^i*(ki1)^(ni1))*Binomial[n1, i], {i, 0, k1}]; Table[t[n, k], {n, 1, 12}, {k, 1, n}] // Flatten (* JeanFrançois Alcover, Jan 22 2015, after Tom Copeland *)
T[ n_, k_] := Coefficient[ n! SeriesCoefficient[ (1  x) Exp[t] / (1  x Exp[ (1  x) t]), {t, 0, n}] // Simplify, x, k]; (* Michael Somos, Jan 22 2015 *)


CROSSREFS

Row sums give A000522.
Cf. A008292, A123125, A248727, A074909, A007318, A000225, A066810, A028246, A001263.
Cf. A119879, A001586.
Cf. A019538, A090582, A123125, A130850.
Sequence in context: A328300 A157152 A136126 * A184173 A022166 A141689
Adjacent sequences: A046799 A046800 A046801 * A046803 A046804 A046805


KEYWORD

nonn,tabl,easy,nice


AUTHOR

N. J. A. Sloane


EXTENSIONS

More terms from Vladeta Jovovic, Sep 20 2003
First formula corrected by Wolfdieter Lang, Feb 14 2015
Title changed by Tom Copeland, Jan 24 2020


STATUS

approved



