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A164559
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a(n) = 6^n/3 - 1.
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4
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1, 11, 71, 431, 2591, 15551, 93311, 559871, 3359231, 20155391, 120932351, 725594111, 4353564671, 26121388031, 156728328191, 940369969151, 5642219814911, 33853318889471, 203119913336831, 1218719480020991, 7312316880125951, 43873901280755711, 263243407684534271
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = 6*a(n-1)+5 for n > 2; a(1) = 1, a(2) = 11.
G.f.: x*(1+4*x)/((1-x)*(1-6*x)).
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PROG
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(Magma) [ 6^n/3-1: n in [1..20] ];
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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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