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A245906
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Numbers of the form 4n^2 + 1 or 4n^2 + 8n + 1.
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0
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5, 13, 17, 33, 37, 61, 65, 97, 101, 141, 145, 193, 197, 253, 257, 321, 325, 397, 401, 481, 485, 573, 577, 673, 677, 781, 785, 897, 901, 1021, 1025, 1153, 1157, 1293, 1297, 1441, 1445, 1597, 1601, 1761, 1765, 1933, 1937, 2113, 2117, 2301, 2305, 2497, 2501, 2701
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OFFSET
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1,1
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LINKS
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FORMULA
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G.f.: x*(5+8*x-6*x^2+x^4)/((1+x)^2*(1-x)^3). [Bruno Berselli, Dec 02 2014]
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MATHEMATICA
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fn[n_]:=Module[{c=4n^2+1}, {c, c+8n}]; Flatten[Array[fn, 30]] (* or *) LinearRecurrence[{1, 2, -2, -1, 1}, {5, 13, 17, 33, 37}, 60] (* Harvey P. Dale, May 21 2015 *)
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PROG
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(PARI) list(lim)=Set(concat(vector(sqrtint((lim-1)\4), n, 4*n^2+1), vector(sqrtint(lim\1+3)\2-1, n, 4*n^2+8*n+1))) \\ Charles R Greathouse IV, Nov 13 2014
(Magma) [IsEven(n) select n^2+4*n+1 else (n+1)^2+1: n in [1..50]]; // Bruno Berselli, Dec 02 2014
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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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