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A204675
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a(n) = 16*n^2 + 2*n + 1.
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3
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1, 19, 69, 151, 265, 411, 589, 799, 1041, 1315, 1621, 1959, 2329, 2731, 3165, 3631, 4129, 4659, 5221, 5815, 6441, 7099, 7789, 8511, 9265, 10051, 10869, 11719, 12601, 13515, 14461, 15439, 16449, 17491, 18565, 19671, 20809, 21979, 23181, 24415, 25681, 26979
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OFFSET
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0,2
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COMMENTS
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Central terms of the triangle A033293.
Also sequence found by reading the line from 1, in the direction 1, 19, ... in the square spiral whose vertices are the generalized decagonal numbers A074377. - Omar E. Pol, Nov 02 2012
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LINKS
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FORMULA
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MATHEMATICA
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CoefficientList[Series[(1+x)*(1+15*x)/(1-x)^3, {x, 0, 50}], x] (* or *) LinearRecurrence[{3, -3, 1}, {1, 19, 69}, 50] (* Vincenzo Librandi, Mar 19 2012 *)
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PROG
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(Haskell)
a204675 n = 2 * n * (8 * n + 1) + 1
(Magma) I:=[1, 19, 69]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+Self(n-3): n in [1..40]]; // Vincenzo Librandi, Mar 19 2012
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CROSSREFS
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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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