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A152813
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a(n) = 2*n^2 + 10*n + 3.
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2
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3, 15, 31, 51, 75, 103, 135, 171, 211, 255, 303, 355, 411, 471, 535, 603, 675, 751, 831, 915, 1003, 1095, 1191, 1291, 1395, 1503, 1615, 1731, 1851, 1975, 2103, 2235, 2371, 2511, 2655, 2803, 2955, 3111, 3271, 3435, 3603, 3775, 3951, 4131, 4315, 4503, 4695
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OFFSET
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0,1
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COMMENTS
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Nonzero x values at solutions of Diophantine equation 2*x^3 + 19*x^2 = y^2.
Nonnegative integers m such that 2*m + 19 is a square. - Vincenzo Librandi, Mar 01 2013
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LINKS
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FORMULA
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Sum_{n>=0} 1/a(n) = 14/45 + tan(sqrt(19)*Pi/2)*Pi/(2*sqrt(19)). - Amiram Eldar, Mar 02 2023
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MATHEMATICA
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CoefficientList[Series[(3 + 6*x - 5*x^2)/(1 - x)^3, {x, 0, 60}], x] (* Vincenzo Librandi, Jan 04 2013 *)
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PROG
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(Magma) I:=[3, 15, 31]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]]; // Vincenzo Librandi, Feb 22 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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EXTENSIONS
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STATUS
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approved
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