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 A084367 a(n) = n*(2*n+1)^2. 2
 0, 9, 50, 147, 324, 605, 1014, 1575, 2312, 3249, 4410, 5819, 7500, 9477, 11774, 14415, 17424, 20825, 24642, 28899, 33620, 38829, 44550, 50807, 57624, 65025, 73034, 81675, 90972, 100949, 111630, 123039, 135200, 148137, 161874 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1). FORMULA a(n) = n*( n*(2*n+1)+1 + n*(2*n+1)+2 + ... + n*(2*n+1)+2*n ). a(n) = n*A016754(n); n*a(n) = A014105(n)^2. G.f.: x*(9+14*x+x^2)/(1-x)^4. - Colin Barker, Jun 30 2012 a(n) = 4*a(n-1) -6*a(n-2) +4*a(n-3) -a(n-4). - Vincenzo Librandi, Jul 04 2012 Sum_{n>=1} 1/a(n) = 4 - 2*log(2) - Pi^2/4. - Amiram Eldar, Jul 21 2020 Sum_{n>=1} (-1)^(n+1)/a(n) = Pi/2 + log(2) + 2*G - 4, where G is Catalan's constant (A006752). - Amiram Eldar, Feb 08 2022 E.g.f.: exp(x)*x*(9 + 16*x + 4*x^2). - Stefano Spezia, Sep 27 2023 EXAMPLE a(3) = 147 since 147 = 3*7^2. MATHEMATICA CoefficientList[Series[x*(9+14*x+x^2)/(1-x)^4, {x, 0, 50}], x] (* Vincenzo Librandi, Jul 04 2012 *) PROG (Magma) I:=[0, 9, 50, 147]; [n le 4 select I[n] else 4*Self(n-1)-6*Self(n-2)+4*Self(n-3)-Self(n-4): n in [1..40]]; // Vincenzo Librandi, Jul 04 2012 CROSSREFS Cf. A006752, A014105, A016754. Sequence in context: A276239 A116169 A280549 * A006974 A279979 A222993 Adjacent sequences: A084364 A084365 A084366 * A084368 A084369 A084370 KEYWORD easy,nonn AUTHOR Charlie Marion, Jun 22 2003 STATUS approved

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Last modified August 5 17:25 EDT 2024. Contains 374953 sequences. (Running on oeis4.)