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Search: id:A130120
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| A130120 |
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a(0)=1. a(n) = number of earlier terms of the sequence which divide n(n+1)/2. |
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+0
2
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| 1, 1, 2, 3, 3, 4, 4, 5, 7, 5, 4, 5, 5, 3, 10, 14, 6, 5, 5, 10, 17, 6, 2, 12, 21, 8, 5, 12, 6, 12, 12, 8, 19, 6, 11, 23, 11, 3, 7, 28, 16, 9, 9, 6, 26, 16, 3, 23, 28, 11, 15, 16, 5, 9, 22, 26, 28, 8, 2, 26, 26, 2, 13, 39, 30, 21, 10, 7, 19, 23, 13, 26, 26, 2, 16, 32, 17, 18, 10, 25, 45, 10, 2
(list; graph; listen)
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OFFSET
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0,3
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EXAMPLE
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a(7)=5 because among the first seven terms of the sequence, namely 1,1,2,3,3,4,4, only 1,1,2,4,and 4 divide 7*8/2=28.
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MAPLE
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a[0]:=1: for n from 1 to 100 do a[n]:=0: for j from 0 to n-1 do if type(n*(n+1)/2/a[j], integer)=true then a[n]:=a[n]+1 else fi: od: od: seq(a[n], n=0..100); - Emeric Deutsch (deutsch(AT)duke.poly.edu), May 22 2007
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MATHEMATICA
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a = {1}; For[n = 1, n < 80, n++, AppendTo[a, Length[Select[(n*(n + 1)/2)/a, IntegerQ[ # ] & ]]]]; a - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Jun 01 2007
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CROSSREFS
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Cf. A130121.
Adjacent sequences: A130117 A130118 A130119 this_sequence A130121 A130122 A130123
Sequence in context: A076895 A029086 A070046 this_sequence A127434 A105677 A103297
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), May 10 2007
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EXTENSIONS
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More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu) and Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), May 22 2007
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