A008281 Triangle of Euler-Bernoulli or Entringer numbers read by rows.

1, 0, 1, 0, 1, 1, 0, 1, 2, 2, 0, 2, 4, 5, 5, 0, 5, 10, 14, 16, 16, 0, 16, 32, 46, 56, 61, 61, 0, 61, 122, 178, 224, 256, 272, 272, 0, 272, 544, 800, 1024, 1202, 1324, 1385, 1385, 0, 1385, 2770, 4094, 5296, 6320, 7120, 7664, 7936, 7936

Offset

0,9

Comments

Zig-Zag numbers (see the Conway and Guy reference p. 110 and the J.-P. Delahaye reference, p. 31).

Approximation to Pi: 2*n*a(n-1,n-1)/a(n,n), n >= 3. See A132049(n)/A132050(n). See the Delahaye reference, p. 31.

The sequence (a(n,n)) of the last element of each row is that of Euler up/down numbers A000111, the Boustrophedon transform of sequence A000007 = (0^n) = (1, 0, 0, 0, ...). - M. F. Hasler, Oct 07 2017

References

J. H. Conway and R. K. Guy, The Book of Numbers, New York: Springer-Verlag, p. 110.

J.-P. Delahaye, Pi - die Story (German translation), Birkhäuser, 1999 Basel, p. 31. French original: Le fascinant nombre Pi, Pour la Science, Paris, 1997.

Links

Vincenzo Librandi and Alois P. Heinz, Rows n = 0..140 (rows n = 0..43 from Vincenzo Librandi)

V. I. Arnold, Bernoulli-Euler updown numbers associated with function singularities, their combinatorics and arithmetics, Duke Math. J. 63 (1991), 537-555.

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), 3-45 = Russian Math. Surveys, Vol. 47 (1992), 1-51.

B. Gourevitch, L'univers de Pi

M. Josuat-Vergès, J.-C. Novelli and J.-Y. Thibon, The algebraic combinatorics of snakes, arXiv preprint arXiv:1110.5272 [math.CO], 2011.

J. Millar, N. J. A. Sloane and N. E. Young, A new operation on sequences: the Boustrophedon transform, J. Combin. Theory, 17A (1996) 44-54 (Abstract, pdf, ps).

C. Poupard, De nouvelles significations énumératives des nombres d'Entringer, Discrete Math., 38 (1982), 265-271.

Heesung Shin and Jiang Zeng, More bijections for Entringer and Arnold families, arXiv:2006.00507 [math.CO], 2020.

OEIS Wiki, Boustrophedon transform.

Formula

a(0,0)=1, a(n,m)=0 if n < m, a(n,m)=0 if m < 0, otherwise a(n,m) = Sum_{k=1..m} a(n-1,n-k).

Example

This version of the triangle begins:
[0] [1]
[1] [0,    1]
[2] [0,    1,    1]
[3] [0,    1,    2,    2]
[4] [0,    2,    4,    5,    5]
[5] [0,    5,   10,   14,   16,   16]
[6] [0,   16,   32,   46,   56,   61,   61]
[7] [0,   61,  122,  178,  224,  256,  272,  272]
[8] [0,  272,  544,  800, 1024, 1202, 1324, 1385, 1385]
[9] [0, 1385, 2770, 4094, 5296, 6320, 7120, 7664, 7936, 7936]
See A008280 and A108040 for other versions.

Maple

A008281 := proc(h, k) option remember ;
    if h=1 and k=1 or h=0 then
        RETURN(1) ;
    elif h>=1 and k> h then
        RETURN(0) ;
    elif h=k then
        RETURN( procname(h, h-1)) ;
    else
        RETURN( add(procname(h-1, j), j=h-k..h-1) ) ;
    fi ;
end: # R. J. Mathar, Nov 27 2006

Mathematica

a[0, 0] = 1; a[n_, m_] /; (n < m || m < 0) = 0; a[n_, m_] := a[n, m] = Sum[a[n-1, n-k], {k, m}]; Flatten[Table[a[n, m], {n, 0, 9}, {m, 0, n}]] (* Jean-François Alcover, May 31 2011, after formula *)

Prog

(Haskell)
a008281 n k = a008281_tabl !! n !! k
a008281_row n = a008281_tabl !! n
a008281_tabl = iterate (scanl (+) 0 . reverse) [1]
-- Reinhard Zumkeller, Sep 10 2013
(Python)
# Python 3.2 or higher required.
from itertools import accumulate
A008281_list = blist = [1]
for _ in range(30):
    blist = [0]+list(accumulate(reversed(blist)))
    A008281_list.extend(blist) # Chai Wah Wu, Sep 18 2014
(Python) from functools import cache
@cache
def seidel(n):
    if n == 0: return [1]
    rowA = seidel(n - 1)
    row = [0] + seidel(n - 1)
    row[1] = row[n]
    for k in range(2, n + 1): row[k] = row[k - 1] + rowA[n - k]
    return row
def A008281row(n): return seidel(n)
for n in range(8): print(A008281row(n)) # Peter Luschny, Jun 01 2022

Crossrefs

Cf. A008280, A000111, A108040.

Sequence in context: A261277 A006462 A278483 * A094671 A354826 A202015

Adjacent sequences: A008278 A008279 A008280 * A008282 A008283 A008284

Keyword

nonn,tabl,nice,easy

Author

N. J. A. Sloane

Status

approved