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 A226489 a(n) = n*(15*n-11)/2. 5
 0, 2, 19, 51, 98, 160, 237, 329, 436, 558, 695, 847, 1014, 1196, 1393, 1605, 1832, 2074, 2331, 2603, 2890, 3192, 3509, 3841, 4188, 4550, 4927, 5319, 5726, 6148, 6585, 7037, 7504, 7986, 8483, 8995, 9522, 10064, 10621, 11193, 11780, 12382, 12999, 13631, 14278 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Sum of n-th 9-gonal (nonagonal) number and n-th 10-gonal (decagonal) number. Sum of reciprocals of a(n), for n>0: 0.614629940137818703272919217222307... LINKS Bruno Berselli, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA G.f.: x*(2+13*x)/(1-x)^3. a(n) + a(-n) = A064761(n). MATHEMATICA Table[n (15 n - 11)/2, {n, 0, 50}] CoefficientList[Series[x (2 + 13 x) / (1 - x)^3, {x, 0, 45}], x] (* Vincenzo Librandi, Aug 18 2013 *) PROG (MAGMA) [n*(15*n-11)/2: n in [0..50]]; (MAGMA) I:=[0, 2, 19]; [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 (PARI) a(n)=n*(15*n-11)/2 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Cf. A001106, A001107. Cf. numbers of the form n*(n*k-k+4))/2, this sequence is the case k=15: see list in A226488. Sequence in context: A307554 A031911 A136685 * A125201 A215392 A140544 Adjacent sequences:  A226486 A226487 A226488 * A226490 A226491 A226492 KEYWORD nonn,easy AUTHOR Bruno Berselli, Jun 09 2013 STATUS approved

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Last modified December 6 04:14 EST 2019. Contains 329784 sequences. (Running on oeis4.)