A060787 - OEIS

%I #28 Jan 01 2025 00:15:19

%S 0,18,108,270,504,810,1188,1638,2160,2754,3420,4158,4968,5850,6804,

%T 7830,8928,10098,11340,12654,14040,15498,17028,18630,20304,22050,

%U 23868,25758,27720,29754,31860,34038,36288,38610,41004,43470,46008,48618,51300,54054,56880,59778

%N a(n) = 18*(n - 2)*(2*n - 5).

%C Except for first term Engel expansion of cosh(1/3); cf. A006784 for Engel expansion definition. - _Benoit Cloitre_, Mar 03 2002

%D L. Berzolari, Allgemeine Theorie der Höheren Ebenen Algebraischen Kurven, Encyclopädie der Mathematischen Wissenschaften mit Einschluss ihrer Anwendungen. Band III_2. Heft 3, Leipzig: B. G. Teubner, 1906. p. 341.

%D H. Brocard and T. Lemoyne, Courbes géométriques remarquables (courbes spéciales) Planes et Gauches. Tome I, Paris: Albert Blanchard, 1967 [First publ. 1919]; see p. 135.

%H Harry J. Smith, <a href="/A060787/b060787.txt">Table of n, a(n) for n = 2..1000</a>

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).

%F G.f.: 18*x^3*(1 + 3*x)/(1 - x)^3. - _Colin Barker_, Feb 29 2012

%o (PARI) a(n) = 18*(n - 2)*(2*n - 5) \\ _Harry J. Smith_, Jul 11 2009

%K nonn,easy

%O 2,2

%A Antreas P. Hatzipolakis (xpolakis(AT)otenet.gr), Apr 28 2001