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 A153792 12 times pentagonal numbers: a(n) = 6*n*(3*n-1). 3
 0, 12, 60, 144, 264, 420, 612, 840, 1104, 1404, 1740, 2112, 2520, 2964, 3444, 3960, 4512, 5100, 5724, 6384, 7080, 7812, 8580, 9384, 10224, 11100, 12012, 12960, 13944, 14964, 16020, 17112, 18240, 19404, 20604, 21840, 23112, 24420 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS For n>=1, a(n) is the first Zagreb index of the triangular grid graph T[n] (see the West reference, p. 390). The first Zagreb index of a simple connected graph is the sum of the squared degrees of its vertices. Alternately, it is the sum of the degree sums d(i)+d(j) over all edges ij of the graph. - Emeric Deutsch, Nov 10 2016 The M-polynomial of the triangular grid graph T[n] is M(T[n], x, y) = 6*x^2*y^4 + 3*(n-1)*x^4*y^4 +6*(n-2)*x^4*y^6+3*(n-2)*(n-3)*x^6*y^6/2. - Emeric Deutsch, May 09 2018 This is the number of overlapping six sphinx tiled shapes in the sphinx tessellated hexagon described in A291582. - Craig Knecht, Sep 13 2017 REFERENCES D. B. West, Introduction to Graph Theory, 2nd edition, Prentice-Hall, 2001. LINKS Harvey P. Dale, Table of n, a(n) for n = 0..1000 E. Deutsch and Sandi Klavzar, M-polynomial and degree-based topological indices, Iranian J. Math. Chemistry, 6, No. 2, 2015, 93-102. Craig Knecht, Example of 12 overlapping shapes in the order 1 hexagon. Eric Weisstein's World of Mathematics, Triangular Grid Graph Index entries for linear recurrences with constant coefficients, signature (3, -3, 1). FORMULA a(n) = 18*n^2 - 6*n = 12*A000326(n) = 6*A049450(n) = 4*A062741(n) = 3*A033579(n) = 2*A152743(n). a(n) = 36*n + a(n-1) - 24 (with a(0)=0). - Vincenzo Librandi, Aug 03 2010 G.f.: 12*x*(1 + 2*x)/(1-x)^3. - Colin Barker, Feb 14 2012 a(0)=0, a(1)=12, a(2)=60; for n>2, a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). - Harvey P. Dale, Mar 11 2012 E.g.f.: 6*x*(2 + 3*x)*exp(x). - G. C. Greubel, Aug 29 2016 a(n) = A291582(n) - A195321(n) for n > 0. - Craig Knecht, Sep 13 2017 MAPLE seq(6*n*(3*n-1), n=0..50); # Robert Israel, Nov 10 2016 MATHEMATICA Table[6n(3n-1), {n, 0, 40}] (* or *) LinearRecurrence[{3, -3, 1}, {0, 12, 60}, 40] (* Harvey P. Dale, Mar 11 2012 *) PROG (PARI) a(n)=6*n*(3*n-1) \\ Charles R Greathouse IV, Jun 17 2017 (GAP) List([0..50], n->6*n*(3*n-1)); # Muniru A Asiru, May 10 2018 CROSSREFS Cf. A000326, A049450, A062741, A033579, A152743, A153449, A153793. Sequence in context: A099829 A099830 A158443 * A229616 A321465 A000141 Adjacent sequences:  A153789 A153790 A153791 * A153793 A153794 A153795 KEYWORD nonn,easy AUTHOR Omar E. Pol, Jan 01 2009 STATUS approved

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Last modified March 28 16:48 EDT 2020. Contains 333089 sequences. (Running on oeis4.)