A294033 Triangle read by rows, expansion of exp(x*z)*z*(tanh(z) + sech(z)), T(n, k) for n >= 1 and 0 <= k <= n-1.

1, 2, 2, -3, 6, 3, -8, -12, 12, 4, 25, -40, -30, 20, 5, 96, 150, -120, -60, 30, 6, -427, 672, 525, -280, -105, 42, 7, -2176, -3416, 2688, 1400, -560, -168, 56, 8, 12465, -19584, -15372, 8064, 3150, -1008, -252, 72, 9, 79360, 124650, -97920, -51240, 20160, 6300, -1680, -360, 90, 10, -555731, 872960, 685575, -359040, -140910, 44352, 11550, -2640, -495, 110, 11

Offset

1,2

Links

Table of n, a(n) for n=1..66.

Formula

T(n, k) = (k+1)*binomial(n,k+1)*2^(n-k-1)*(Euler(n-k-1, 1/2) + Euler(n-k-1, 1))) for 0 <= k <= n-2.

T(n, k) is the coefficient of x^k of the polynomial p(n) = n*Sum_{k=1..n} binomial(n-1, k-1)*L(k-1)*x^(n-k) and L(n) = (-1)^binomial(n,2)*A000111(n). In particular n divides T(n, k).

Example

Triangle starts:
[1][   1]
[2][   2,   2]
[3][  -3,   6,    3]
[4][  -8, -12,   12,    4]
[5][  25, -40,  -30,   20,    5]
[6][  96, 150, -120,  -60,   30,  6]
[7][-427, 672,  525, -280, -105, 42, 7]

Maple

gf := exp(x*z)*z*(tanh(z)+sech(z)):
s := n -> n!*coeff(series(gf, z, n+2), z, n):
C := n -> PolynomialTools:-CoefficientList(s(n), x):
ListTools:-FlattenOnce([seq(C(n), n=1..7)]);
# Alternatively:
T := (n, k) -> `if`(n = k+1, n,
(k+1)*binomial(n, k+1)*2^(n-k-1)*(euler(n-k-1, 1/2)+euler(n-k-1, 1))):
for n from 1 to 7 do seq(T(n, k), k=0..n-1) od;

Mathematica

L[0] := 1; L[n_] := (-1)^Binomial[n, 2] 2 Abs[PolyLog[-n, -I]];
p[n_] := n Sum[Binomial[n - 1, k - 1] L[k - 1] x^(n - k), {k, 0, n}];
Table[CoefficientList[p[n], x], {n, 1, 11}] // Flatten

Crossrefs

T(n, 0) = signed A065619. Row sums of abs(T(n,k)) = A231179.

Diagonals A000027, A002378, A027480, A162668.

A003506 (m=1), this seq. (m=2), A294034 (m=3).

Cf. A000111, A247453.

Sequence in context: A209420 A317449 A222310 * A376168 A254827 A193862

Adjacent sequences: A294030 A294031 A294032 * A294034 A294035 A294036

Keyword

sign,tabl

Author

Peter Luschny, Oct 24 2017

Status

approved