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A237617
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a(n) = n*(n + 1)*(17*n - 14)/6.
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2
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0, 1, 20, 74, 180, 355, 616, 980, 1464, 2085, 2860, 3806, 4940, 6279, 7840, 9640, 11696, 14025, 16644, 19570, 22820, 26411, 30360, 34684, 39400, 44525, 50076, 56070, 62524, 69455, 76880, 84816, 93280, 102289, 111860, 122010, 132756, 144115, 156104, 168740
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OFFSET
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0,3
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COMMENTS
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Also 19-gonal (or nonadecagonal) pyramidal numbers.
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REFERENCES
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E. Deza and M. M. Deza, Figurate numbers, World Scientific Publishing (2012), page 93 (seventeenth row of the table).
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LINKS
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FORMULA
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G.f.: x*(1 + 16*x)/(1 - x)^4.
For n>0, a(n) = Sum_{i=0..n-1} (n-i)*(17*i+1); see the generalization in A237616 (Formula field).
E.g.f.: x*(6 + 54*x + 17*x^2)*exp(x)/6. - G. C. Greubel, Aug 30 2019
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EXAMPLE
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After 0, the sequence is provided by the row sums of the triangle:
1;
2, 18;
3, 36, 35;
4, 54, 70, 52;
5, 72, 105, 104, 69;
6, 90, 140, 156, 138, 86;
7, 108, 175, 208, 207, 172, 103;
8, 126, 210, 260, 276, 258, 206, 120;
9, 144, 245, 312, 345, 344, 309, 240, 137;
10, 162, 280, 364, 414, 430, 412, 360, 274, 154; etc.,
where (r = row index, c = column index):
T(r,r) = T(c,c) = 17*r - 16 and T(r,c) = T(r-1,c) + T(r,r) = (r-c+1) * T(r,r), with r>=c>0.
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MAPLE
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MATHEMATICA
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Table[n(n+1)(17*n-14)/6, {n, 0, 40}]
CoefficientList[Series[x(1+16x)/(1-x)^4, {x, 0, 40}], x] (* Vincenzo Librandi, Feb 12 2014 *)
LinearRecurrence[{4, -6, 4, -1}, {0, 1, 20, 74}, 40] (* Harvey P. Dale, Aug 04 2021 *)
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PROG
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(Magma) [n*(n+1)*(17*n-14)/6: n in [0..40]];
(Magma) I:=[0, 1, 20, 74]; [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, Feb 12 2014
(PARI) vector(40, n, n*(n-1)*(17*n-31)/6) \\ G. C. Greubel, Aug 30 2019
(Sage) [n*(n+1)*(17*n-14)/6 for n in (0..40)] # G. C. Greubel, Aug 30 2019
(GAP) List([0..40], n-> n*(n+1)*(17*n-14)/6); # G. C. Greubel, Aug 30 2019
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CROSSREFS
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Cf. similar sequences listed in A237616.
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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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