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A014901
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a(1)=1, a(n) = 18*a(n-1) + n.
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2
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1, 20, 363, 6538, 117689, 2118408, 38131351, 686364326, 12354557877, 222382041796, 4002876752339, 72051781542114, 1296932067758065, 23344777219645184, 420205989953613327, 7563707819165039902, 136146740744970718253
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OFFSET
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1,2
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LINKS
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FORMULA
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a(1)=1, a(2)=20, a(3)=363, a(n) = 20*a(n-1) - 37*a(n-2) + 18*a(n-3). - Vincenzo Librandi, Oct 20 2012
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MATHEMATICA
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LinearRecurrence[{20, -37, 18}, {1, 20, 363}, 20] (* Vincenzo Librandi, Oct 20 2012 *)
nxt[{n_, a_}]:={n+1, 18a+n+1}; NestList[nxt, {1, 1}, 20][[All, 2]] (* Harvey P. Dale, Oct 08 2017 *)
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PROG
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(Magma) I:=[1, 20, 363]; [n le 3 select I[n] else 20*Self(n-1) - 37*Self(n-2) + 18*Self(n-3): n in [1..20]]; // Vincenzo Librandi, Oct 20 2012
(Maxima)
a[1]:1$
a[2]:20$
a[3]:363$
a[n]:=20*a[n-1]-37*a[n-2]+18*a[n-3]$
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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