OFFSET
1,5
COMMENTS
Horizontal position is x-coordinate of the start of the leftmost horizontal step of the first peak.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..500
A. Blecher, C. Brennan, and A. Knopfmacher, Peaks in bargraphs, Trans. Royal Soc. South Africa, 71, No. 1, 2016, 97-103.
FORMULA
G.f.: (2*x^3*(x^2-sqrt(x^4+2*x^2-4*x+1)+1)) / ((1-x)*(-x^2+sqrt(x^4+2*x^2-4*x+1)-2*x+1)^2).
EXAMPLE
For n = 4, a(4) = 1, as only the bargraph with first column of height one and second column of height two has horizontal position 1, all other cases are zero.
PROG
(PARI) seq(n) = my(r=sqrt((1 - x)*(1 - 3*x - x^2 - x^3) + O(x^(n-2)))); Vec(2*x^3*(1 + x^2 - r) / ((1 - x)*(1 - 2*x - x^2 + r)^2), -n) \\ Andrew Howroyd, Jan 12 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Arnold Knopfmacher, Nov 07 2016
STATUS
approved