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Search: id:A131845
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| A131845 |
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a(1)=a(2)=1. a(n) = number of terms of the sequence (from among terms a(1) through a(n-1)) which divide (a(n-1)*a(n-2)). |
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+0
1
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| 1, 1, 2, 3, 4, 5, 5, 4, 7, 6, 6, 8, 9, 10, 10, 9, 12, 11, 10, 9, 14, 11, 7, 6, 10, 16, 13, 8, 8, 9, 17, 8, 10, 17, 12, 13, 13, 5, 8, 18, 22, 19, 7, 6, 12, 23, 14, 9, 19, 10, 14, 20, 26, 24, 24, 27, 27, 10, 26, 21, 20, 32, 24, 23, 23, 5, 9, 13, 13, 7, 11, 9, 13, 16, 20, 27, 38, 22, 13, 17
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OFFSET
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1,3
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EXAMPLE
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a(11)*a(12) = 6*8 = 48. The terms, from among the first 12 terms of the sequence, which divide 48 are: a(1)=1, a(2)=1, a(3)=2, a(4)=3, a(5)=4, a(8)=4, a(10)=6, a(11)=6, and a(12)=8. There are 9 such terms, so a(13) = 9.
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MAPLE
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a[1]:=1: a[2]:=1: for n from 3 to 70 do a[n]:=0: for i to n-1 do if type(a[n-1]*a[n-2]/a[i], integer)=true then a[n]:=a[n]+1 else end if end do end do: seq(a[n], n=1..70); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Oct 16 2007
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MATHEMATICA
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a = {1, 1}; Do[AppendTo[a, Length[Select[Range[Length[a]], Mod[a[[ -1]]*a[[ -2]], a[[ # ]]] == 0 &]]], {80}]; a - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Oct 07 2007
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CROSSREFS
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Sequence in context: A101916 A100771 A113771 this_sequence A062186 A085763 A062985
Adjacent sequences: A131842 A131843 A131844 this_sequence A131846 A131847 A131848
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (q1qq2qqq3qqqq(AT)yahoo.com), Oct 04 2007
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EXTENSIONS
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More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Oct 07 2007
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