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A134455
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a(0) = a(1) = 1, a(2) = 2; a(n) = 2*a(n-2) + a(n-1)*a(n-3).
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0
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1, 1, 2, 4, 8, 24, 112, 944, 22880, 2564448, 2420884672, 55389846424256, 142044380887832220032, 343873064435082883562892998016, 19047076228497528742755382412205052966716160
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OFFSET
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0,3
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COMMENTS
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This is a recurrence relation which has 1,1 and 2 as the base cases and the n-th term is obtained by multiplying the (n-2)th term by 2 and adding it with the product of (n-1)th and (n-3)rd term.
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LINKS
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FORMULA
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a(n) ~ c^(d^n), where d = 1.465571231876768026... is the root of the equation d^3 = d^2 + 1 and c = 1.604048928929157460568... . - Vaclav Kotesovec, Oct 01 2015
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MAPLE
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f:=proc(n) option remember;
if n <= 1 then 1 elif n=2 then 2 else
f(n-1)*f(n-3)+2*f(n-2); fi; end;
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MATHEMATICA
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RecurrenceTable[{a[0]==a[1]==1, a[2]==2, a[n]==2a[n-2]+a[n-1]a[n-3]}, a, {n, 20}] (* Harvey P. Dale, Oct 01 2015 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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Mohit Maheshwari (mohitmahe1989(AT)gmail.com), Jan 19 2008
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EXTENSIONS
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STATUS
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approved
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