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 A004068 Number of atoms in a decahedron with n shells. 27
 0, 1, 7, 23, 54, 105, 181, 287, 428, 609, 835, 1111, 1442, 1833, 2289, 2815, 3416, 4097, 4863, 5719, 6670, 7721, 8877, 10143, 11524, 13025, 14651, 16407, 18298, 20329, 22505, 24831, 27312, 29953, 32759, 35735, 38886, 42217, 45733, 49439 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Also as a(n)=(n/6)*(5*n^2+1), n>0: structured pentagonal diamond numbers (vertex structure 6) (cf. A081436 = alternate vertex; A000447 = structured diamonds; A100145 for more on structured numbers). - James A. Record (james.record(AT)gmail.com), Nov 07 2004 Number of atoms in decahedron with n shells, number = 5/6*(n^3) + 1/6*(n) (T. P. Martin, Shells of atoms, eq.(3)). - Brigitte Stepanov, Jul 02 2011 a(n+1) is the number of triples (w,x,y) having all terms in {0,...,n} and x+y>=w. - Clark Kimberling, Jun 14 2012 a(n) = Sum_{k=1..n} A215630(n,k) for n > 0. - Reinhard Zumkeller, Nov 11 2012 a(n) - a(n-2) = A010001(n-1), for n>1. - K. G. Stier, Dec 21 2012 a(n) is also a figurate number representing a cube of side n with a vertex cut off by a tetrahedron of side n-1. As such, a(n) = A000578(n) - A000292(n-1), n > 0. - Jean M. Morales, Aug 11 2013 The sequence starting with 1 is the third partial sum of (1, 4, 5, 5, 5,...) and the binomial transform of (1, 6, 10, 5, 0, 0, 0,...). - Gary W. Adamson, Sep 27 2015 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..5000 T. P. Martin, Shells of atoms, Phys. Reports, 273 (1996), 199-241, eq. (3). Index entries for linear recurrences with constant coefficients, signature (4, -6, 4, -1). FORMULA a(n) = 5*binomial(n + 1, 3) + binomial(n, 1). a(n) = 5*n^3/6 + n/6. a(n) = Sum_{i=0..n-1} A005891(i). - Xavier Acloque, Oct 08 2003 G.f. x*(1+3*x+x^2) / (1-x)^4. - R. J. Mathar, Jun 05 2011 E.g.f.: (x/6)*(5x^2 + 15x + 6)*exp(x). - G. C. Greubel, Sep 27 2015 MATHEMATICA Table[5*n^3/6+n/6, {n, 0, 80}] (* Vladimir Joseph Stephan Orlovsky, Apr 18 2011 *) PROG (MAGMA) [5*n^3/6+n/6: n in [0..50]]; // Vincenzo Librandi, May 15 2011 (Maxima) A004068(n):=5*n^3/6+n/6\$ makelist(A004068(n), n, 0, 20); /* Martin Ettl, Jan 07 2013 */ (PARI) a(n)=5*n^3/6+n/6 \\ Charles R Greathouse IV, Sep 24 2015 CROSSREFS 1/12*t*(n^3-n)+n for t = 2, 4, 6, ... gives A004006, A006527, A006003, A005900, A004068, A000578, A004126, A000447, A004188, A004466, A004467, A007588, A062025, A063521, A063522, A063523. Cf. A005891, A006322. Sequence in context: A098334 A038796 A211791 * A261893 A022815 A172252 Adjacent sequences:  A004065 A004066 A004067 * A004069 A004070 A004071 KEYWORD nonn,easy AUTHOR Albert D. Rich (Albert_Rich(AT)msn.com) EXTENSIONS Typo in definition corrected by Jean M. Morales, Aug 11 2013 STATUS approved

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