A125597 a(1)=1; a(n) = Sum_{1<=k<n, gcd(k,n(n+1)/2)=1} a(k).

1, 1, 1, 2, 4, 8, 6, 11, 21, 51, 11, 22, 133, 159, 151, 328, 707, 1414, 880, 1732, 3850, 9482, 1742, 3480, 22126, 37243, 25604, 51381, 102087, 204174, 157324, 285010, 660221, 1285026, 262885, 547906, 3664304, 5844380, 3927062, 8543954, 19956539

Offset

1,4

Links

Robert Israel, Table of n, a(n) for n = 1..5397

Example

The positive integers < 8 and coprime to 8*9/2 = 36 are 1,5,7. So a(8) = a(1)+a(5)+a(7) = 1+4+6 = 11.

Maple

A[1]:= 1:
for n from 2 to 100 do
  A[n]:= add(A[j], j=select(k -> igcd(k, n*(n+1)/2)=1, [$1..n-1]))
od:
seq(A[i], i=1..100); # Robert Israel, Mar 28 2018

Mathematica

f[l_List] := Block[{n = Length[l] + 1}, Append[l, Plus @@ l[[Select[Range[n - 1], GCD[ #, n*(n + 1)/2] == 1 &]]]]]; Nest[f, {1}, 40] (* Ray Chandler, Nov 26 2006 *)

Crossrefs

Cf. A125596.

Sequence in context: A121711 A249681 A256561 * A366170 A151732 A109554

Adjacent sequences: A125594 A125595 A125596 * A125598 A125599 A125600

Keyword

nonn

Author

Leroy Quet, Nov 26 2006

Extensions

Extended by Ray Chandler, Nov 26 2006

Status

approved