%I #11 Aug 02 2019 20:10:41
%S 1,1,1,2,1,2,3,5,4,9,5,10,12,18,21,48,22,44,48,88,84,197,92,183,260,
%T 432,441,908,183,366,1178,1800,1778,3743,1541,3346,5627,8913,7159,
%U 16638,7429,14858,24107,38702,38615,88520,40509,79474,88596,167790,169580
%N a(1)=1. a(n) = Sum_{1<=k<n, gcd(k,n(n+1))=1} a(k).
%e The positive integers < 8 and coprime to 8 and 9 are 1,5,7. So a(8) = a(1) + a(5) + a(7) = 1+1+3 = 5.
%t f[l_List] := Block[{n = Length[l] + 1},Append[l, Plus @@ l[[Select[Range[n], GCD[ #, n*(n + 1)] == 1 &]]]]];Nest[f, {1}, 50] (* _Ray Chandler_, Nov 26 2006 *)
%Y Cf. A125597.
%K nonn
%O 1,4
%A _Leroy Quet_, Nov 26 2006
%E Extended by _Ray Chandler_, Nov 26 2006