

A001586


Generalized Euler numbers, or Springer numbers.
(Formerly M2908 N1169)


40



1, 1, 3, 11, 57, 361, 2763, 24611, 250737, 2873041, 36581523, 512343611, 7828053417, 129570724921, 2309644635483, 44110959165011, 898621108880097, 19450718635716001, 445777636063460643, 10784052561125704811, 274613643571568682777, 7342627959965776406281
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OFFSET

0,3


COMMENTS

From Peter Bala, Feb 02 2011: (Start)
The Springer numbers were originally considered by Glaisher (see references). They are a type B analog of the zigzag numbers A000111 for the group of signed permutations.
COMBINATORIAL INTERPRETATIONS
Several combinatorial interpretations of the Springer numbers are known:
1) a(n) gives the number of Weyl chambers in the principal Springer cone of the Coxeter group B_n of symmetries of an n dimensional cube. An example can be found in [Arnold  The Calculus of snakes...].
2) Arnold found an alternative combinatorial interpretation of the Springer numbers in terms of snakes. Snakes are a generalization of alternating permutations to the group of signed permutations. A signed permutation is a sequence (x_1,x_2,...,x_n) of integers such that {x_1,x_2,...,x_n} = {1,2,...,n}. They form a group, the hyperoctahedral group of order 2^n*n! = A000165(n), isomorphic to the group of symmetries of the n dimensional cube. A snake of type B_n is a signed permutation (x_1,x_2,...,x_n) such that 0 < x_1 > x_2 < ... x_n. For example, (3,4,2,5,1,6) is a snake of type B_6. a(n) gives the number of snakes of type B_n [Arnold]. The cases n=2 and n=3 are given in the Example section below.
3) The Springer numbers also arise in the study of the critical points of functions; they count the topological types of odd functions with 2*n critical values [Arnold, Theorem 35].
4) Let F_n be the set of plane rooted forests satisfying the following conditions:
... each root has exactly one child, and each of the other internal nodes has exactly two (ordered) children,
... there are n nodes labeled by integers from 1 to n, but some leaves can be nonlabeled (these are called empty leaves), and labels are increasing from each root down to the leaves. Then a(n) equals the cardinality of F_n. An example and proof are given in [Verges, Theorem 4.5].
OTHER APPEARANCES OF THE SPRINGER NUMBERS
1) Hoffman has given a connection between Springer numbers, snakes and the successive derivatives of the secant and tangent functions.
2) For integer N the quarter Gauss sums Q(N) are defined by ... Q(N) := Sum_{r = 0..floor(N/4)} exp(2*Pi*I*r^2/N). In the cases N = 1 (mod 4) and N = 3 (mod 4) an asymptotic series for Q(N) as N > inf that involves the Springer numbers has been given by Evans et al., see 1.32 and 1.33.
For a sequence of polynomials related to the Springer numbers see A185417. For a table to recursively compute the Springer numbers see A185418.
(End)
Similar to the way in which the signed Euler numbers A122045 are 2^n times the value of the Euler polynomials at 1/2, the generalized signed Euler numbers A188458 can be seen as 2^n times the value of generalized Euler polynomials at 1/2. These are the SwissKnife polynomials A153641. A recursive definition of these polynomials is given in A081658.  Peter Luschny, Jul 19 2012
a(n) is the number of reversecomplementary updown permutations of [2n]. For example, the updown permutation 241635 is reversecomplementary because its complement is 536142, which is the same as its reverse, and a(2)=3 counts 1324, 2413, 3412.  David Callan, Nov 29 2012
a(n) = 2^n G(n,1/2;1), a specialization of the Appell sequence of polynomials umbrally formed by G(n,x;t) = (G(.,0;t) + x)^n from the Grassmann polynomials G(n,0;t) of A046802 enumerating the cells of the positive Grassmannians.  Tom Copeland, Oct 14 2015


REFERENCES

V. I. Arnold, Springer numbers and Morsification spaces. J. Algebraic Geom. 1 (1992), no. 2, 197214.
J. W. L. Glaisher, "On the coefficients in the expansions of cos x/cos 2x and sin x/cos 2x", Quart. J. Pure and Applied Math., 45 (1914), 187222.
J. W. L. Glaisher, On the Bernoullian function, Q. J. Pure Appl. Math., 29 (1898), 1168.
Ulrike Sattler, Decidable classes of formal power series with nice closure properties, Diplomarbeit im Fach Informatik, Univ. Erlangen  Nuernberg, Jul 27 1994
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
T.A. Springer, Remarks on a combinatorial problem, Nieuw Arch. Wisk. 19(3) (1971), 3036.


LINKS

T. D. Noe, Table of n, a(n) for n=0..100
V. I. Arnold, The calculus of snakes and the combinatorics of Bernoulli, Euler and Springer numbers of Coxeter groups, Uspekhi Mat. nauk., 47 (#1, 1992), 345 = Russian Math. Surveys, Vol. 47 (1992), 151. English version.
P. Barry, A Note on Three Families of Orthogonal Polynomials defined by Circular Functions, and Their Moment Sequences, Journal of Integer Sequences, Vol. 15 (2012), #12.7.2.
Paul Barry, On a transformation of Riordan moment sequences, arXiv:1802.03443 [math.CO], 2018.
W. Y. C. Chen, N. J. Y. Fan and J. Y. T. Jia, Labeled Ballot Paths and the Springer Numbers, arXiv:1009.2233 [math.CO], Sep 12 2010. [From Jonathan Vos Post, Sep 13 2010]
Suyoung Choi, B. Park, H. Park, The Betti numbers of real toric varieties associated to Weyl chambers of type B, arXiv preprint arXiv:1602.05406, 2016.
C.O. Chow and S.M. Ma, Counting signed permutations by their alternating runs, Discrete Mathematics, Volume 323, 28 May 2014, Pages 4957.
D. Dumont, Further triangles of SeidelArnold type and continued fractions related to Euler and Springer numbers Adv. Appl. Math., 16 (1995), 275296.
R. Evans, M. Minei and B. Yee, Incomplete higher order Gauss sums (see 1.32 and 1.33) J. Math. Anal. Appl., 281(2):454476, 2003.
Dominique Foata and GuoNiu Han, Multivariable Tangent and Secant qderivative Polynomials, see also arXiv:1304.2486 [math.CO].
J. W. L. Glaisher, On a set of coefficients analogous to the Eulerian numbers, Proc. London Math. Soc., 31 (1899), 216235.
M. E. Hoffman, Derivative Polynomials, Euler Polynomials, and Associated Integer Sequences, The Electronic Journal of Combinatorics 6 (1999), #R21 (see Th. 3.1).
M. JosuatVerges, Enumeration of snakes and cyclealternating permutations, arXiv:1011.0929 [math.CO], 2010.
M. JosuatVerges, J.C. Novelli and J.Y. Thibon, The algebraic combinatorics of snakes, arXiv preprint arXiv:1110.5272 [math.CO], 2011
I. Pak, A. Soffer, On Higman's k(U_n(F_q)) conjecture, arXiv preprint arXiv:1507.00411, 2015
D. Shanks, Generalized Euler and class numbers, Math. Comp. 21 (1967), 689694; 22 (1968), 699. [Annotated scanned copy]
D. Shanks, Generalized Euler and class numbers. Math. Comp. 21 (1967) 689694.
D. Shanks, Corrigenda to: "Generalized Euler and class numbers", Math. Comp. 21 (1967), 689694; 22 (1968), 699.
Alan D. Sokal, The Euler and Springer numbers as moment sequences, arXiv:1804.04498 [math.CO], 2018.
ZhiHong Sun, Congruences involving Bernoulli polynomials, Discr. Math., 308 (2007), 71112.
Z.W. Sun, Conjectures involving arithmetical sequences, Number Theory: Arithmetic in ShangriLa (eds., S. Kanemitsu, H.Z. Li and J.Y. Liu), Proc. the 6th ChinaJapan Sem. Number Theory (Shanghai, August 1517, 2011), World Sci., Singapore, 2013, pp. 244258; see Conjectures involving combinatorial sequences, arXiv preprint arXiv:1208.2683 [math.CO], 2012.
A. Vieru, Agoh's conjecture: its proof, its generalizations, its analogues, arXiv preprint arXiv:1107.2938 [math.NT], 2011.


FORMULA

E.g.f.: 1/(cos(x)  sin(x)).
Values at 1 of polynomials Q_n() defined in A104035.  N. J. A. Sloane, Nov 06 2009
a(n) = numerator of abs(Euler(n,1/4)).  N. J. A. Sloane, Nov 07 2009
Let B_n(x) = Sum_{k=0.. n*(n1)/2} b(n,k)*x^k, where b(n,k) is number of nnode acyclic digraphs with k arcs, cf. A081064; then a(n) = B_n(2).  Vladeta Jovovic, Jan 25 2005
G.f. A(x) = y satisfies y'^2 = 2y^4  y^2, y''y = y^2 + 2y'^2.  Michael Somos, Feb 03 2004
a(n) = (1)^floor(n/2) Sum_{k=0..n} 2^k C(n,k) Euler(k).  Peter Luschny, Jul 08 2009
From Peter Bala, Feb 02 2011: (Start)
(1)... a(n) = ((1 + i)/2)^n*B(n,(1  i)/(1 + i)), where i = sqrt(1) and {B(n,x)}n>=0 = [1, 1 + x, 1 + 6*x + x^2, 1 + 23*x + 23*x^2 + x^3, ...] is the sequence of type B Eulerian polynomials  see A060187.
This yields the explicit formula
(2)... a(n) = ((1 + i)/2)^n*Sum_{k = 0..n} ((1  i)/(1 + i))^k * Sum_{j = 0..k} (1)^(kj)*binomial(n+1,kj)*(2*j + 1)^n.
The result (2) can be used to find congruences satisfied by the Springer numbers. For example, for odd prime p
(3)
... a(p) = 1 (mod p) when p = 4*n + 1
... a(p) = 1 (mod p) when p = 4*n + 3.
(End)
E.g.f.: 1/Q(0) where Q(k)=1x/((2k+1)x*(2k+1)/(x+(2k+2)/Q(k+1))); (continued fraction).  Sergei N. Gladkovskii, Nov 19 2011
E.g.f.: 2/U(0) where U(k)= 1 + 1/(1 + x/(2*k + 1 x  (2*k+1)/(2  x/(x+ (2*k+2)/U(k+1))))) ; (continued fraction, 5step).  Sergei N. Gladkovskii, Sep 24 2012
E.g.f.: 1/G(0) where G(k) = 1  x/(4*k+1  x*(4*k+1)/(4*k+2 + x + x*(4*k+2)/(4*k+3  x  x*(4*k+3)/(x + (4*k+4)/G(k+1) )))); (continued fraction, 3rd kind, 5step).  Sergei N. Gladkovskii, Oct 02 2012
G.f.: 1/G(0) where G(k) = 1  x*(2*k+1)  2*x^2*(k+1)*(k+1)/G(k+1); (continued fraction).  Sergei N. Gladkovskii, Jan 11 2013
a(n) =  2*4^n*lerchphi(1, n, 1/4) .  Peter Luschny, Apr 27 2013
a(n) ~ 4 * n^(n+1/2) * (4/Pi)^n / (sqrt(Pi)*exp(n)).  Vaclav Kotesovec, Oct 07 2013
G.f.: T(0)/(1x), where T(k) = 1  2*x^2*(k+1)^2/( 2*x^2*(k+1)^2  (1x2*x*k)*(13*x2*x*k)/T(k+1) ); (continued fraction).  Sergei N. Gladkovskii, Oct 15 2013
a(n) = (1)^C(n+1,2)*2^(3*n+1)*(Zeta(n,1/8)Zeta(n,5/8)), where Zeta(a,z) is the generalized Riemann zeta function.  Peter Luschny, Mar 11 2015
E.g.f. A(x) satisfies: A(x) = exp( Integral A(x)/A(x) dx ).  Paul D. Hanna, Feb 04 2017
E.g.f. A(x) satisfies: A'(x) = A(x)^2/A(x).  Paul D. Hanna, Feb 04 2017


EXAMPLE

Example
a(2) = 3: The three snakes of type B_2 are
(1,2), (2,1), (2,1).
a(3) = 11: The 11 snakes of type B_3 are
(1,2,3), (1,3,2), (1,3,2),
(2,1,3), (2,1,3), (2,3,1), (2,3,1),
(3,1,2), (3,1,2), (3,2,1), (3,2,1).


MAPLE

a := proc(n) local k; (1)^iquo(n, 2)*add(2^k*binomial(n, k)*euler(k), k=0..n) end; # Peter Luschny, Jul 08 2009
a := n > (1)^(n+iquo(n, 2))*2^(3*n+1)*(Zeta(0, n, 1/8)  Zeta(0, n, 5/8)):
seq(a(n), n=0..21); # Peter Luschny, Mar 11 2015


MATHEMATICA

n=21; CoefficientList[Series[1/(Cos[x]Sin[x]), {x, 0, n}], x] * Table[k!, {k, 0, n}] (* JeanFrançois Alcover, May 18 2011 *)
Table[Abs[Numerator[EulerE[n, 1/4]]], {n, 0, 35}] (* Harvey P. Dale, May 18 2011 *)


PROG

(PARI) {a(n) = if(n<0, 0, n! * polcoeff( 1 / (cos(x + x * O(x^n))  sin(x + x * O(x^n))), n))}; /* Michael Somos, Feb 03 2004 */
(PARI) {a(n) = my(an); if(n<2, n>=0, an = vector(n+1, m, 1); for(m=2, n, an[m+1] = 2*an[m] + an[m1] + sum(k=0, m3, binomial(m2, k) * (an[k+1] * an[m1k] + 2*an[k+2] * an[mk]  an[k+3] * an[m1k]))); an[n+1])}; /* Michael Somos, Feb 03 2004 */
(PARI) /* Explicit formula by Peter Bala: */
{a(n)=((1+I)/2)^n*sum(k=0, n, ((1I)/(1+I))^k*sum(j=0, k, (1)^(kj)*binomial(n+1, kj)*(2*j+1)^n))}
(Sage)
@CachedFunction
def p(n, x) :
if n == 0 : return 1
w = 1 if n%2 == 0 else 0
v = 1 if n%2 == 0 else 1
return v*add(p(k, 0)*binomial(n, k)*(x^(nk)+w) for k in range(n)[::2])
def A001586(n) : return abs(2^n*p(n, 1/2))
[A001586(n) for n in (0..21)] # Peter Luschny, Jul 19 2012


CROSSREFS

Cf. A007836, A079858, A185417, A185418, A212435.
Bisections are A000281 and A000464.
Related polynomials are given in A098432, A081658 and A153641.
Cf. A046802.
Sequence in context: A180112 A188458 A212435 * A126201 A261643 A229512
Adjacent sequences: A001583 A001584 A001585 * A001587 A001588 A001589


KEYWORD

nonn,easy,nice


AUTHOR

N. J. A. Sloane


EXTENSIONS

More terms from Vladeta Jovovic, Jan 25 2005


STATUS

approved



