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 A004126 a(n) = n*(7*n^2 - 1)/6. 21
 0, 1, 9, 31, 74, 145, 251, 399, 596, 849, 1165, 1551, 2014, 2561, 3199, 3935, 4776, 5729, 6801, 7999, 9330, 10801, 12419, 14191, 16124, 18225, 20501, 22959, 25606, 28449, 31495, 34751, 38224, 41921, 45849, 50015, 54426, 59089, 64011 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS 3-dimensional analog of centered polygonal numbers. Sum of n triangular numbers starting from T(n), where T = A000217. E.g., a(4) = T(4) + T(5) + T(6) + T(7) = 10 + 15 + 21 + 28 = 74. - Amarnath Murthy, Jul 16 2004 Also as a(n) = (1/6)*(7*n^3-n), n>0: structured heptagonal diamond numbers (vertex structure 8). Cf. A100179 = alternate vertex; A000447 = structured diamonds; A100145 for more on structured numbers. - James A. Record (james.record(AT)gmail.com), Nov 07 2004 Partial sums of A069099, centered heptagonal numbers (A000566). - Jonathan Vos Post, Mar 16 2006 Binomial transform of (0, 1, 7, 7, 0, 0, 0, ...) and third partial sum of (0, 1, 6, 7, 7, 7, ...). - Gary W. Adamson, Oct 05 2015 REFERENCES E. Deza and M. M. Deza, Figurate numbers, World Scientific Publishing (2012), page 140. 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. (11). Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1). FORMULA a(n) = C(2*n+1,3)-C(n+1,3), n>=0. - Zerinvary Lajos, Jan 21 2007 a(n) = A000447(n) - A000292(n). - Zerinvary Lajos, Jan 21 2007 G.f.: x*(1+5*x+x^2)/(1-x)^4. - Colin Barker, Mar 02 2012 E.g.f.: (x/6)*(7*x^2 + 21*x + 6)*exp(x). - G. C. Greubel, Oct 05 2015 a(n) = Sum_{i = n..2*n-1} A000217(i). - Bruno Berselli, Sep 06 2017 a(n) = n^3 + Sum_{k=0..n-1} k*(k+1)/2. Alternately, a(n) = A000578(n) + A000292(n-1) for n>0. - Bruno Berselli, May 23 2018 MAPLE seq(binomial(2*n+1, 3)-binomial(n+1, 3), n=0..38); # Zerinvary Lajos, Jan 21 2007 MATHEMATICA Table[n (7 n^2 - 1)/6, {n, 0, 80}] (* Vladimir Joseph Stephan Orlovsky, Apr 18 2011 *) PROG (MAGMA) [n*(7*n^2-1)/6: n in [0..50]]; // Vincenzo Librandi, May 15 2011 (Maxima) makelist(n*(7*n^2-1)/6, n, 0, 30); /* Martin Ettl, Jan 08 2013 */ (PARI) vector(100, n, n--; n*(7*n^2 - 1)/6) \\ Altug Alkan, Oct 06 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. A000217, A000566, A016993, A069099. Cf. A000447, A000292. Sequence in context: A266397 A288419 A168297 * A177342 A224000 A118444 Adjacent sequences:  A004123 A004124 A004125 * A004127 A004128 A004129 KEYWORD nonn,easy AUTHOR Albert D. Rich (Albert_Rich(AT)msn.com) STATUS approved

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Last modified April 22 22:19 EDT 2021. Contains 343197 sequences. (Running on oeis4.)