OFFSET
1,2
COMMENTS
Inspired by a formula in the reference, the study of the singular points of planar differential systems leads to 3 two-dimensional polynomial families, one ordinary (degenerate case, considered in one dimension, see A129326) and two odd (the second, considered in one dimension, see A129587).
The first is in one dimension P(2n-1,x)=(n+1+x^n)*sum_{i=0..n-1} x^i/(i+1), n>=1.
The table of coefficients of P() with 2n coefficients per row starts:
2, 1;
3, 3/2, 1, 1/2;
4, 2, 4/3, 1, 1/2, 1/3;.. .
Rows multiplied by n!, the table becomes Q():
2, 1;
6, 3, 2, 1;
24, 12, 8, 6, 3, 2;
120, 60, 40, 30, 24, 12, 8, 6;
720, 360, 240, 180, 144,...
The sequence gives the alternating row sums of this table Q, positive sign for coefficients in front of even and negative sign for coefficients in front of odd powers of x.
The row sums of Q are (n+2)*A000254(n)= 3, 12, 55, 300...
Adding the alternating and ordinary row sums yields the sequence 4, 16, 70, 384....
The sequence of sums of antidiagonals in the Q table starts 2, 6+1=7, 24+3=27, 120+12+1=134.
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..250
Jean-François Alcover, Roots of P(2n-1,x) lie close to a circle (example)
P. Curtz, Stabilité locale des systèmes quadratiques, Ann. Sc. Ec. Norm. Sup., vol. 13 no. 3 (1980) 293-302.
FORMULA
EXAMPLE
a(1) = 2-1.
a(2) = 6-3+2-1.
a(3) = 24-12+8-6+3-2.
MATHEMATICA
a[n_] := (1/2)*(n + (-1)^n + 1)*n!*((-1)^n*(HarmonicNumber[(n-1)/2] - HarmonicNumber[n/2]) + Log[4]); Table[a[n] // FullSimplify, {n, 1, 19}] (* Jean-François Alcover, Oct 03 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul Curtz, Jun 29 2007
EXTENSIONS
Edited and extended by R. J. Mathar, Jul 28 2008
STATUS
approved