This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A277973 #16 Jan 12 2024 17:25:35 %S A277973 0,0,0,1,6,25,91,311,1029,3346,10778,34544,110444,352785,1126885, %T A277973 3601617,11521648,36899528,118322448,379908707,1221423149,3932113059, %U A277973 12675055399,40909511880,132200481507,427718677728,1385419058692,4492446685542,14582927712740,47385785436719 %N A277973 Sum of horizontal positions of the first peak in all bargraphs of semiperimeter n. %C A277973 Horizontal position is x-coordinate of the start of the leftmost horizontal step of the first peak. %H A277973 Andrew Howroyd, <a href="/A277973/b277973.txt">Table of n, a(n) for n = 1..500</a> %H A277973 A. Blecher, C. Brennan, and A. Knopfmacher, <a href="http://dx.doi.org/10.1080/0035919X.2015.1059905">Peaks in bargraphs</a>, Trans. Royal Soc. South Africa, 71, No. 1, 2016, 97-103. %F A277973 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). %e A277973 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. %o A277973 (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 %Y A277973 Cf. A271941, A273720, A273345, A277999. %K A277973 nonn %O A277973 1,5 %A A277973 _Arnold Knopfmacher_, Nov 07 2016