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 A028569 a(n) = n*(n + 9). 21
 0, 10, 22, 36, 52, 70, 90, 112, 136, 162, 190, 220, 252, 286, 322, 360, 400, 442, 486, 532, 580, 630, 682, 736, 792, 850, 910, 972, 1036, 1102, 1170, 1240, 1312, 1386, 1462, 1540, 1620, 1702, 1786, 1872, 1960, 2050, 2142, 2236, 2332, 2430 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS a(n) is the first Zagreb index of the wheel graph with n + 1 vertices. 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 07 2016 The sequence provides all nonnegative k such that 4*k + 81 is a square. - Bruno Berselli, May 08 2018 LINKS Shawn A. Broyles, Table of n, a(n) for n = 0..1000 Patrick De Geest, Palindromic Quasipronics of the form n(n+x). Felix Pozon Muga II, Extending the Golden Ratio and the Binet-de Moivre Formula, Preprint on ResearchGate, March 2014. Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA Equals 2 * A056000. - Zerinvary Lajos, Feb 12 2007 a(n) = 2*n + a(n - 1) + 8. - Vincenzo Librandi, Aug 05 2010 Sum_{n >= 1} 1/a(n) = 7129/22680 = 0.314329806... - R. J. Mathar, Mar 22 2011 G.f.: 2*x*(5 - 4*x)/(1 - x)^3. - Colin Barker, Jan 10 2012 a(n) = 3*a(n - 1) - 3*a(n - 2) + a(n - 3). - Wesley Ivan Hurt, Sep 26 2014 Sum_{n>=1} (-1)^(n+1)/a(n) = 2*log(2)/9 - 1879/22680. - Amiram Eldar, Jan 15 2021 MAPLE A028569:=n->n*(n+9): seq(A028569(n), n=0..50); # Wesley Ivan Hurt, Sep 26 2014 MATHEMATICA Table[n (n + 9), {n, 0, 50}] (* Wesley Ivan Hurt, Sep 26 2014 *) PROG (MAGMA) [n*(n+9) : n in [0..50]]; // Wesley Ivan Hurt, Sep 26 2014 (PARI) a(n)=n*(n+9) \\ Charles R Greathouse IV, Sep 24 2015 (Scala) (0 to 49).map(n => n * (n + 9)) // Alonso del Arte, Apr 22 2020 CROSSREFS Cf. A056000. Sequence in context: A276626 A211482 A177791 * A014367 A063710 A157917 Adjacent sequences:  A028566 A028567 A028568 * A028570 A028571 A028572 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified May 17 22:15 EDT 2021. Contains 343992 sequences. (Running on oeis4.)