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 A086020 a(n) = Sum_(i=1..n) C(i+2,3)^2 [ Sequential sums of the tetragonal numbers or "tetras" (pyramidal, square) raised to power 2 (drawn from the 4th diagonal - left or right - of Pascal's Triangle) ]. 26
 1, 17, 117, 517, 1742, 4878, 11934, 26334, 53559, 101959, 183755, 316251, 523276, 836876, 1299276, 1965132, 2904093, 4203693, 5972593, 8344193, 11480634, 15577210, 20867210, 27627210, 36182835, 46915011, 60266727, 76750327 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Kekulé numbers for certain benzenoids (see the Cyvin-Gutman reference, p. 243; expression in (13.26) yields same sequence with offset 0). - Emeric Deutsch, Aug 02 2005 Partial sums of A001249. - R. J. Mathar, Aug 19 2008 LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988. John Engbers and Christopher Stocker, Two Combinatorial Proofs of Identities Involving Sums of Powers of Binomial Coefficients, Integers 16 (2016), #A58. Index entries for linear recurrences with constant coefficients, signature (8,-28,56,-70,56,-28,8,-1). FORMULA a(n) = Sum_(i=1..n) C(i+2, 3)^2. a(n) = ( C(n+3, 4)/35 )*( 35 +84*C(n-1, 1) +70*C(n-1, 2) +20*C(n-1, 3) ). a(n) = n*(n+1)*(n+2)*(n+3)*(2*n+3)(5*n^2 +15*n +1)/2520. - Emeric Deutsch, Aug 02 2005 O.g.f: x*(1+x)*(1 +8*x +x^2)/(1-x)^8. - R. J. Mathar, Aug 19 2008 EXAMPLE a(8) = Sum_{i=1..8} C(i+2,3)^2 = (20*(8^7) + 210*(8^6) + 854*(8^5) + 1680*(8^4) + 1610*(8^3) + 630*(8^2) + 36*8)/7! = 26334. MAPLE a:=n->n*(n+1)*(n+2)*(n+3)*(2*n+3)*(5*n^2+15*n+1)/2520: seq(a(n), n=1..31); # Emeric Deutsch MATHEMATICA Accumulate[Binomial[Range[30]+2, 3]^2]  (* Harvey P. Dale, Mar 24 2011 *) LinearRecurrence[{8, -28, 56, -70, 56, -28, 8, -1}, {1, 17, 117, 517, 1742, 4878, 11934, 26334}, 30] (* Harvey P. Dale, Aug 17 2014 *) PROG (PARI) a(n)=n*(n+1)*(n+2)*(n+3)*(2*n+3)*(5*n^2+15*n+1)/2520 \\ Charles R Greathouse IV, May 18 2015 (MAGMA) [n*(n+1)*(n+2)*(n+3)*(2*n+3)*(5*n^2+15*n+1)/2520: n in [1..30]]; // G. C. Greubel, Nov 22 2017 CROSSREFS Cf. A000292, A087127, A024166, A085438, A085439, A085440, A085441, A085442, A000332, A086021, A086022, A000389, A086023, A086024, A000579, A086025, A086026, A000580, A086027, A086028, A027555, A086029, A086030. Sequence in context: A293877 A044349 A044730 * A056117 A196575 A003109 Adjacent sequences:  A086017 A086018 A086019 * A086021 A086022 A086023 KEYWORD easy,nice,nonn AUTHOR André F. Labossière, Jul 17 2003 STATUS approved

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Last modified December 4 22:42 EST 2021. Contains 349526 sequences. (Running on oeis4.)