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A226450
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a(n) = n*(3*n^2 - 5*n + 3).
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3
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0, 1, 10, 45, 124, 265, 486, 805, 1240, 1809, 2530, 3421, 4500, 5785, 7294, 9045, 11056, 13345, 15930, 18829, 22060, 25641, 29590, 33925, 38664, 43825, 49426, 55485, 62020, 69049, 76590, 84661, 93280, 102465, 112234, 122605, 133596, 145225, 157510, 170469
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OFFSET
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0,3
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COMMENTS
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For n >= 3, also the detour index of the n-barbell graph. - Eric W. Weisstein, Dec 20 2017
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LINKS
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FORMULA
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G.f.: x*(1+6*x+11*x^2)/(1-x)^4.
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MATHEMATICA
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Table[n (3 n^2 - 5 n + 3), {n, 0, 40}]
CoefficientList[Series[x (1 + 6 x + 11 x^2)/(1 - x)^4, {x, 0, 40}], x] (* Vincenzo Librandi, Aug 18 2013 *)
LinearRecurrence[{4, -6, 4, -1}, {1, 10, 45, 124}, {0, 20}] (* Eric W. Weisstein, Dec 20 2017 *)
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PROG
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(Magma) [n*(3*n^2-5*n+3): n in [0..40]];
(Magma) I:=[0, 1, 10, 45]; [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..45]]; // Vincenzo Librandi, Aug 18 2013
(PARI) a(n) = n*(3*n^2 - 5*n + 3); \\ Altug Alkan, Dec 20 2017
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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