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
KEYWORD
nonn
AUTHOR
Leroy Quet, Nov 26 2006
EXTENSIONS
Extended by Ray Chandler, Nov 26 2006
STATUS
approved