A129456 - OEIS

%I #12 Feb 10 2019 23:03:19

%S 1,1,2,3,4,4,3,4,2,9,10,8,5,3,14,15,16,12,2,12,8,21,22,13,24,23,24,17,

%T 16,17,30,31,20,33,34,22,15,15,38,34,17,18,8,23,44,45,43,10,21,15,39,

%U 10,23,25,54,55,36,35,36,44,26,39,62,49,64,41,66,61,43,29,41,31,72,58,21

%N a(0)=1. a(n) is the number of earlier terms of the sequence that are coprime to (n+a(n-1)).

%e 11 + a(10) = 21. There are 8 terms among a(0), a(1), ..., a(10) that are coprime to 21. (These terms are a(0), a(1), a(2), a(4), a(5), a(7), a(8) and a(10).) So a(11) = 8.

%p a[0]:=1: for n from 1 to 120 do ct:=0: for i from 0 to n-1 do if igcd(a[i],n+a[n-1])=1 then ct:=ct+1 else ct:=ct: fi: od: a[n]:=ct: od: seq(a[n],n=0..100); # _Emeric Deutsch_, May 05 2007

%Y Cf. A129457.

%K nonn

%O 0,3

%A _Leroy Quet_, Apr 16 2007

%E More terms from _Emeric Deutsch_, May 05 2007