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 A152751 3 times octagonal numbers: 3*n*(3*n-2). 19
 0, 3, 24, 63, 120, 195, 288, 399, 528, 675, 840, 1023, 1224, 1443, 1680, 1935, 2208, 2499, 2808, 3135, 3480, 3843, 4224, 4623, 5040, 5475, 5928, 6399, 6888, 7395, 7920, 8463, 9024, 9603, 10200, 10815, 11448, 12099, 12768, 13455 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS a(n) also can be represented as n concentric triangles (see example). - Omar E. Pol, Aug 21 2011 LINKS Ivan Panchenko, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = 9*n^2 - 6*n = A000567(n)*3 = A064201(n)/3. a(n) = a(n-1) + 18*n - 15 with n>0, a(0)=0. - Vincenzo Librandi, Nov 26 2010 G.f.: 3*x*(1+5*x)/(1-x)^3. - Bruno Berselli, Jan 21 2011 EXAMPLE From Omar E. Pol, Aug 21 2011: (Start) Illustration of initial terms as concentric triangles: . .                                          o .                                         o o .                                        o   o .                                       o     o .                 o                    o   o   o .                o o                  o   o o   o .               o   o                o   o   o   o .              o     o              o   o     o   o .    o        o   o   o            o   o   o   o   o .   o o      o   o o   o          o   o   o o   o   o .           o           o        o   o           o   o .          o o o o o o o o      o   o o o o o o o o   o .                              o                       o .                             o o o o o o o o o o o o o o . .    3            24                       63 (End) MATHEMATICA s=0; lst={s}; Do[s+=n; AppendTo[lst, s], {n, 3, 6!, 18}]; lst (* Vladimir Joseph Stephan Orlovsky, Apr 02 2009 *) PROG (PARI) a(n)=3*n*(3*n-2) \\ Charles R Greathouse IV, Sep 24 2015 CROSSREFS Cf. A000567, A064201, A139267. 3 times n-gonal numbers: A045943, A033428, A062741, A094159, A152773, A152759, A152767, A153783, A153448, A153875. Cf. A033581, A085250, A152734, A194273. - Omar E. Pol, Aug 21 2011 Cf. numbers of the form n*(n*k-k+6))/2, this sequence is the case k=18: see Comments lines of A226492. Sequence in context: A101008 A070734 A009113 * A162654 A092468 A027158 Adjacent sequences:  A152748 A152749 A152750 * A152752 A152753 A152754 KEYWORD easy,nonn AUTHOR Omar E. Pol, Dec 12 2008 STATUS approved

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