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A182751
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a(1) = 1; a(2) = 3; a(3) = 6; a(n) = 3*a(n-2) for n > 3.
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8
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1, 3, 6, 9, 18, 27, 54, 81, 162, 243, 486, 729, 1458, 2187, 4374, 6561, 13122, 19683, 39366, 59049, 118098, 177147, 354294, 531441, 1062882, 1594323, 3188646, 4782969, 9565938, 14348907, 28697814, 43046721, 86093442, 129140163
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OFFSET
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1,2
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COMMENTS
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For n >= 3: a(n) = the smallest number > a(n-1) such that ((a(n-2)+a(n-1)) * (a(n-2) + a(n)) * (a(n-1) + a(n))) / (a(n-2) * a(n-1) * a(n)) is integer (= 10 for n >= 4).
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LINKS
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Harvey P. Dale, Table of n, a(n) for n = 1..1000
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FORMULA
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a(n) = A038754(n) for n >= 2.
a(2n) = 3/2 * a(2n-1) for n>=2, a(2n+1) = 2 * a(2n).
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EXAMPLE
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For n = 5; a(3) = 6, a(4) = 9, a(5) = 18 before [(6+9)*(6+18)*(9+18)] / (6*9*18) = 10.
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MATHEMATICA
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Join[{1}, RecurrenceTable[{a[2]==3, a[3]==6, a[n]==3a[n-2]}, a[n], {n, 50}]] (* or *) Transpose[NestList[{#[[2]], #[[3]], 3#[[2]]}&, {1, 3, 6}, 49]][[1]] (* From Harvey P. Dale, Oct 19 2011 *)
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CROSSREFS
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Cf. A182752 - A182757. Essentially the same as A038754 (cf. formula).
Sequence in context: A007783 A050625 A025614 * A057576 A100852 A059006
Adjacent sequences: A182748 A182749 A182750 * A182752 A182753 A182754
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KEYWORD
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nonn,easy,less
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AUTHOR
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Jaroslav Krizek, Nov 27 2010
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STATUS
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approved
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