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A134927
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a(0)=a(1)=1; a(n) = 3*(a(n-1) + a(n-2)).
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1
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1, 1, 6, 21, 81, 306, 1161, 4401, 16686, 63261, 239841, 909306, 3447441, 13070241, 49553046, 187869861, 712268721, 2700415746, 10238053401, 38815407441, 147160382526, 557927369901, 2115263257281, 8019571881546, 30404505416481
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OFFSET
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0,3
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LINKS
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FORMULA
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O.g.f.: (-1+2*x)/(-1 + 3*x + 3*x^2).
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MAPLE
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a[0]:=1:a[1]:=1:for n from 2 to 50 do a[n]:=3*a[n-1]+3*a[n-2] od: seq(a[n], n=0..33); # Zerinvary Lajos, Dec 14 2008
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MATHEMATICA
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LinearRecurrence[{3, 3}, {1, 1}, 30]
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PROG
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(Sage)
from sage.combinat.sloane_functions import recur_gen2
it = recur_gen2(1, 1, 3, 3)
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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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