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A010009
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a(0) = 1, a(n) = 19*n^2 + 2 for n>0.
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1
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1, 21, 78, 173, 306, 477, 686, 933, 1218, 1541, 1902, 2301, 2738, 3213, 3726, 4277, 4866, 5493, 6158, 6861, 7602, 8381, 9198, 10053, 10946, 11877, 12846, 13853, 14898, 15981, 17102, 18261, 19458, 20693, 21966, 23277, 24626, 26013, 27438, 28901, 30402, 31941
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OFFSET
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0,2
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COMMENTS
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Apart from the first term, numbers of the form (r^2+2*s^2)*n^2+2 = (r*n)^2+(s*n-1)^2+(s*n+1)^2: in this case is r=1, s=3. After 1, all terms are in A000408. - Bruno Berselli, Feb 06 2012
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LINKS
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FORMULA
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MATHEMATICA
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Join[{1}, LinearRecurrence[{3, -3, 1}, {21, 78, 173}, 50]] (* Vincenzo Librandi, Aug 03 2015 *)
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PROG
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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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