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A182751 a(1) = 1; a(2) = 3; a(3) = 6; a(n) = 3*a(n-2) for n > 3. 8
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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).

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A038754(n) for n >= 2.

a(2n) = 3/2 * a(2n-1) for n>=2, a(2n+1) = 2 * a(2n).

EXAMPLE

For n = 5; a(3) = 6, a(4) = 9, a(5) = 18 before [(6+9)*(6+18)*(9+18)]  / (6*9*18) = 10.

MATHEMATICA

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]] (* Harvey P. Dale, Oct 19 2011 *)

CROSSREFS

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

KEYWORD

nonn,easy,less

AUTHOR

Jaroslav Krizek, Nov 27 2010

STATUS

approved

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Last modified July 26 01:07 EDT 2014. Contains 244923 sequences.