A130121 a(1)=1. a(n) = number of earlier terms of the sequence which divide n(n+1)/2.

1, 1, 2, 3, 3, 4, 4, 7, 4, 2, 6, 7, 4, 6, 12, 8, 4, 4, 4, 10, 6, 2, 18, 19, 2, 4, 14, 9, 4, 4, 17, 23, 5, 6, 19, 14, 4, 6, 27, 19, 6, 6, 6, 20, 7, 3, 30, 35, 7, 7, 18, 6, 7, 8, 29, 41, 9, 3, 22, 22, 2, 14, 47, 23, 7, 6, 8, 24, 17, 11, 37, 37, 4, 9, 27, 23, 14, 6, 25, 50, 12, 3, 34, 41, 5, 8, 41

Offset

1,3

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

a[1]:=1: for n from 2 to 110 do a[n]:=0: for j from 1 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=1..110); # Emeric Deutsch, May 19 2007

Mathematica

s={1}; Do[c=0; Do[If[Divisible[n(n+1)/2, s[[i]]], c++], {i, n-1}]; AppendTo[s, c], {n, 2, 87}]; s (* James C. McMahon, Feb 06 2025 *)

Crossrefs

Cf. A130120.

Sequence in context: A320052 A168173 A095916 * A007898 A372594 A367009

Adjacent sequences: A130118 A130119 A130120 * A130122 A130123 A130124

Keyword

nonn

Author

Leroy Quet, May 10 2007

Extensions

More terms from Emeric Deutsch, May 19 2007

Status

approved