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A303813
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Generalized 19-gonal (or enneadecagonal) numbers: m*(17*m - 15)/2 with m = 0, +1, -1, +2, -2, +3, -3, ...
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31
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0, 1, 16, 19, 49, 54, 99, 106, 166, 175, 250, 261, 351, 364, 469, 484, 604, 621, 756, 775, 925, 946, 1111, 1134, 1314, 1339, 1534, 1561, 1771, 1800, 2025, 2056, 2296, 2329, 2584, 2619, 2889, 2926, 3211, 3250, 3550, 3591, 3906, 3949, 4279, 4324, 4669, 4716, 5076, 5125, 5500, 5551, 5941, 5994, 6399
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OFFSET
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0,3
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COMMENTS
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Numbers k for which 136*k + 225 is a square. - Bruno Berselli, Jul 10 2018
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LINKS
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FORMULA
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G.f.: x*(1 + 15*x + x^2) / ((1 - x)^3*(1 + x)^2).
a(n) = (34*n^2 + 60*n)/16 for n even.
a(n) = (34*n^2 + 8*n - 26)/16 for n odd.
a(n) = a(n-1) + 2*a(n-2) - 2*a(n-3) - a(n-4) + a(n-5) for n>4.
(End)
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MATHEMATICA
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With[{nn = 54}, {0}~Join~Riffle[Array[PolygonalNumber[19, #] &, Ceiling[nn/2]], Array[PolygonalNumber[19, -#] &, Ceiling[nn/2]]]] (* Michael De Vlieger, Jun 06 2018 *)
CoefficientList[ Series[-x (x^2 + 15x + 1)/((x - 1)^3 (x + 1)^2), {x, 0, 50}], x] (* or *)
LinearRecurrence[{1, 2, -2, -1, 1}, {0, 1, 16, 19, 49}, 51] (* Robert G. Wilson v, Jul 28 2018 *)
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PROG
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(PARI) concat(0, Vec(x*(1 + 15*x + x^2) / ((1 - x)^3*(1 + x)^2) + O(x^40))) \\ Colin Barker, Jun 08 2018
(GAP) a:=[0, 1, 16, 19, 49];; for n in [6..60] do a[n]:=a[n-1]+2*a[n-2]-2*a[n-3]-a[n-4]+a[n-5]; od; a; # Muniru A Asiru, Jul 10 2018
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CROSSREFS
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Sequences of generalized k-gonal numbers: A001318 (k=5), A000217 (k=6), A085787 (k=7), A001082 (k=8), A118277 (k=9), A074377 (k=10), A195160 (k=11), A195162 (k=12), A195313 (k=13), A195818 (k=14), A277082 (k=15), A274978 (k=16), A303305 (k=17), A274979 (k=18), this sequence (k=19), A218864 (k=20), A303298 (k=21), A303299 (k=22), A303303 (k=23), A303814 (k=24), A303304 (k=25), A316724 (k=26), A316725 (k=27), A303812 (k=28), A303815 (k=29), A316729 (k=30).
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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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