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A226490
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a(n) = n*(19*n-15)/2.
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4
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0, 2, 23, 63, 122, 200, 297, 413, 548, 702, 875, 1067, 1278, 1508, 1757, 2025, 2312, 2618, 2943, 3287, 3650, 4032, 4433, 4853, 5292, 5750, 6227, 6723, 7238, 7772, 8325, 8897, 9488, 10098, 10727, 11375, 12042, 12728, 13433, 14157, 14900, 15662, 16443, 17243
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OFFSET
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0,2
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COMMENTS
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Sum of n-th hendecagonal number and n-th dodecagonal number.
Sum of reciprocals of a(n), for n>0: 0.59314195720519963010713286193275...
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LINKS
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FORMULA
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G.f.: x*(2+17*x)/(1-x)^3.
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MATHEMATICA
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Table[n (19 n - 15)/2, {n, 0, 50}]
CoefficientList[Series[x (2 + 17 x) / (1 - x)^3, {x, 0, 45}], x] (* Vincenzo Librandi, Aug 18 2013 *)
LinearRecurrence[{3, -3, 1}, {0, 2, 23}, 50] (* Harvey P. Dale, Aug 17 2017 *)
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PROG
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(Magma) [n*(19*n-15)/2: n in [0..50]];
(Magma) I:=[0, 2, 23]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+Self(n-3): n in [1..45]]; // Vincenzo Librandi, Aug 18 2013
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CROSSREFS
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Cf. numbers of the form n*(n*k-k+4))/2, this sequence is the case k=19: see list in A226488.
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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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