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 A116204 a(0) = 1; for n >= 1, a(n) = the number of positive divisors of n which are coprime to a(n-1). 2

%I

%S 1,1,2,2,1,2,2,2,1,3,4,2,2,2,2,4,1,2,3,2,2,4,2,2,2,3,4,4,2,2,4,2,1,4,

%T 2,4,3,2,2,4,2,2,4,2,2,6,2,2,2,3,6,2,2,2,4,4,2,4,2,2,4,2,2,6,1,4,4,2,

%U 2,4,4,2,3,2,2,6,2,4,4,2,2,5,4,2,4,4,2,4,2,2,6,4,2,4,2,4,2,2,3,2,3,2,4,2,2

%N a(0) = 1; for n >= 1, a(n) = the number of positive divisors of n which are coprime to a(n-1).

%e a(11) = 2. There are 2 positive divisors (1 and 3) of 12 which are coprime to 2. So a(12) = 2.

%p with(numtheory): a[0]:=1: for n from 1 to 140 do ct:=0: div:=divisors(n): for j from 1 to tau(n) do if igcd(div[j],a[n-1])=1 then ct:=ct+1 else ct:=ct: fi: od: a[n]:=ct: od: seq(a[n],n=0..140); # _Emeric Deutsch_, Apr 27 2007

%p A116204 := proc(nmax) local a,n,dvs,resl,d ; a := [1] ; while nops(a) < nmax do n := nops(a) ; dvs := numtheory[divisors](n) ; resl :=0 ; for d from 1 to nops(dvs) do if gcd(op(d,dvs), op(-1,a)) = 1 then resl := resl+1 ; fi ; od ; a := [op(a),resl] ; od ; RETURN(a) ; end: A116204(100) ; # _R. J. Mathar_, Apr 27 2007

%K nonn

%O 0,3

%A _Leroy Quet_, Apr 16 2007

%E More terms from _R. J. Mathar_ and _Emeric Deutsch_, Apr 27 2007

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Last modified October 13 23:25 EDT 2019. Contains 327983 sequences. (Running on oeis4.)