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A096113 a(1) = 1, a(2) = 2; then all new products of subsets of pre-existing terms, then the first integer not present, and so on. 7
1, 2, 3, 6, 4, 8, 12, 18, 24, 36, 48, 72, 144, 5, 10, 15, 16, 20, 30, 32, 40, 54, 60, 64, 80, 90, 96, 108, 120, 160, 180, 192, 216, 240, 270, 288, 320, 324, 360, 384, 432, 480, 540, 576, 648, 720, 768, 864, 960, 1080, 1152, 1296, 1440, 1536, 1620, 1728, 1920, 1944 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Another rearrangement of the natural numbers.
Description: the iterative extension of the sequence is a loop over the steps: (i) Select the smallest integer not yet in the sequence and append it. (ii) Compute a set of all products of two or more distinct factors taken from the current, finite version of the sequence. (iii) Remove members from this set that are already in the sequence. Append the sorted list of the numbers in the set to the sequence. Return to (i). - R. J. Mathar, Feb 21 2009
LINKS
EXAMPLE
a(3) = 3 because all products of {1, 2} are already included. The only new product generated by {1, 2, 3} is 6, then 4 is the first integer which doesn't appear. Then {1, 2, 3, 6, 4} generates 8 (=2*4), 12 (=2*6=3*4), 18 (=3*6), 24 (=6*4=2*3*4), 36 (=2*3*6), 48 (=2*6*4), 72 (=3*6*4) and 144 (=2*3*6*4). Then the next term is 5. And so on.
MATHEMATICA
L[1]={1} L[n_]:=L[n]=Join[L[n-1], Complement[Union[Exp[Map[ Total, Log[Subsets[Delete[L[n-1], 1]]]]]], L[n-1]], {n}] L[6]
CROSSREFS
Sequence in context: A086537 A212486 A127562 * A110797 A083872 A121663
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Jun 29 2004
EXTENSIONS
Edited by Joel B. Lewis, Nov 15 2006
STATUS
approved

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Last modified March 19 06:29 EDT 2024. Contains 370953 sequences. (Running on oeis4.)