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A307559
a(n) = floor(n/3)*(n - floor(n/3))*(n - floor(n/3) - 1).
0
0, 0, 2, 6, 12, 24, 40, 60, 90, 126, 168, 224, 288, 360, 450, 550, 660, 792, 936, 1092, 1274, 1470, 1680, 1920, 2176, 2448, 2754, 3078, 3420, 3800, 4200, 4620, 5082, 5566, 6072, 6624, 7200, 7800, 8450, 9126, 9828, 10584, 11368, 12180, 13050, 13950, 14880, 15872
OFFSET
1,3
COMMENTS
a(n) is an upper bound for the irregularity of a graph with n vertices (see Theorem 3.2 of the Tavakoli et al. reference).
LINKS
M. Tavakoli, F. Rahbarnia, M. Mirzavaziri, A. R. Ashrafi, and I. Gutman, Extremely irregular graphs, Kragujevac J. Math., 37 (1), 2013, 135-139.
FORMULA
a(n) = 2*A200067(n).
G.f.: 2*x^3*(1+x)*(1+x^2) / ( (1+x+x^2)^2*(x-1)^4 ). - R. J. Mathar, Jul 22 2022
EXAMPLE
a(4) = floor(4/3)*(4 - floor(4/3))*(4-floor(4/3)-1) = 1*3*2 = 6.
MAPLE
a:=n->floor(n/3)*(n-floor(n/3))*(n-floor(n/3)-1): seq(a(n), n=1..50);
CROSSREFS
Cf. A200067.
Sequence in context: A307252 A306625 A262986 * A211978 A028923 A187272
KEYWORD
nonn,easy
AUTHOR
Emeric Deutsch, Apr 14 2019
STATUS
approved