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Search: id:A087955
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| A087955 |
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a(n) is the square of the n-th partial sum minus the n-th partial sum of the squares, divided by a(n-1), for all n>=1, starting with a(0)=1, a(1)=2. |
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+0
4
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| 1, 2, 2, 8, 12, 34, 62, 152, 304, 698, 1458, 3248, 6924, 15210, 32734, 71440, 154432, 336018, 727874, 1581496, 3429100, 7445714, 16151518, 35059560, 76068400, 165095562, 358241202, 777459488, 1687087532, 3661224794, 7945027902
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OFFSET
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0,2
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FORMULA
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a(n) = a(n-1) + 3a(n-2) - a(n-3) for n>3; G.f.: (1+x-3x^2+x^3)/(1-x-3x^2+x^3).
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EXAMPLE
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a(4)=12 since ((1+2+2+8)^2 - (1^2+2^2+2^2+8^2))/8 = (13^2-73)/8 = 12.
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CROSSREFS
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Sequence in context: A008828 A053414 A014236 this_sequence A026537 A089248 A006663
Adjacent sequences: A087952 A087953 A087954 this_sequence A087956 A087957 A087958
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KEYWORD
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nonn
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AUTHOR
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Paul D. Hanna (pauldhanna(AT)juno.com), Sep 16 2003
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