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 A257602 Expansion of (1 + x + 21*x^2 + x^3 + x^4)/(1 - x)^5. 1
 1, 6, 41, 156, 426, 951, 1856, 3291, 5431, 8476, 12651, 18206, 25416, 34581, 46026, 60101, 77181, 97666, 121981, 150576, 183926, 222531, 266916, 317631, 375251, 440376, 513631, 595666, 687156, 788801, 901326, 1025481, 1162041, 1311806, 1475601, 1654276, 1848706, 2059791, 2288456, 2535651 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS If x is replaced by x^5, this is the Molien series for the Heisenberg group H(5). LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 Yang-Hui He and John McKay, Sporadic and Exceptional, arXiv:1505.06742 [math.AG], 2015. Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1). FORMULA G.f.: (1 + x + 21*x^2 + x^3 + x^4)/(1-x)^5. a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5). - Vincenzo Librandi, Jun 08 2015 a(n) = (25/24)*n^4 + (25/12)*n^3 + (35/24)*n^2 + (5/12)*n + 1 = 1 + 5*n*(n+1)*(5*n^2 + 5*n + 2)/24 = 1 + 5*A006322(n). - R. J. Mathar, Nov 09 2018 E.g.f.: (1/24)*(24 + 120*x + 360*x^2 + 200*x^3 + 25*x^4)*exp(x). - G. C. Greubel, Mar 24 2022 MATHEMATICA CoefficientList[Series[(1 +x +21x^2 +x^3 +x^4)/(1-x)^5, {x, 0, 40}], x] (* Vincenzo Librandi, Jun 08 2015 *) LinearRecurrence[{5, -10, 10, -5, 1}, {1, 6, 41, 156, 426}, 40] (* Harvey P. Dale, Dec 01 2017 *) PROG (Magma) I:=[1, 6, 41, 156, 426]; [n le 5 select I[n] else 5*Self(n-1)-10*Self(n-2)+10*Self(n-3)-5*Self(n-4)+Self(n-5): n in [1..45]]; // Vincenzo Librandi, Jun 08 2015 (Sage) [1 + 5*n*(n+1)*(5*n^2+5*n+2)/24 for n in (0..50)] # G. C. Greubel, Mar 24 2022 CROSSREFS Sequence in context: A354331 A000611 A043069 * A135232 A371536 A291890 Adjacent sequences: A257599 A257600 A257601 * A257603 A257604 A257605 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Jun 07 2015 STATUS approved

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Last modified August 12 08:23 EDT 2024. Contains 375085 sequences. (Running on oeis4.)