A130120 a(0)=1. a(n) = number of earlier terms of the sequence that divide n(n+1)/2.

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

Offset

0,3

Links

Table of n, a(n) for n=0..82.

Example

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.

Maple

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, May 22 2007

Mathematica

a = {1}; For[n = 1, n < 80, n++, AppendTo[a, Length[Select[(n*(n + 1)/2)/a, IntegerQ[ # ] & ]]]]; a (* Stefan Steinerberger, Jun 01 2007 *)

Crossrefs

Cf. A130121.

Sequence in context: A282029 A029086 A070046 * A204892 A164512 A127434

Adjacent sequences: A130117 A130118 A130119 * A130121 A130122 A130123

Keyword

nonn

Author

Leroy Quet, May 10 2007

Extensions

More terms from Emeric Deutsch and Stefan Steinerberger, May 22 2007

Status

approved