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A154600
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a(n) = 2*n^2 + 22*n + 9.
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2
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33, 61, 93, 129, 169, 213, 261, 313, 369, 429, 493, 561, 633, 709, 789, 873, 961, 1053, 1149, 1249, 1353, 1461, 1573, 1689, 1809, 1933, 2061, 2193, 2329, 2469, 2613, 2761, 2913, 3069, 3229, 3393, 3561, 3733, 3909, 4089, 4273, 4461, 4653, 4849, 5049, 5253
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OFFSET
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1,1
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COMMENTS
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2*a(n) + 103 is a square.
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LINKS
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FORMULA
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G.f: x*(-33 + 38*x - 9*x^2)/(x-1)^3.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). (End)
Sum_{n>=1} 1/a(n) = 257162/3084939 + tan(sqrt(103)*Pi/2)*Pi/(2*sqrt(103)). - Amiram Eldar, Feb 25 2023
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MATHEMATICA
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PROG
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(Magma) I:=[33, 61, 93]; [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 26 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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