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a(1) = 0, then after the first differences of A003434.
2

%I #14 Aug 18 2024 16:04:38

%S 0,1,1,0,1,-1,1,0,0,0,1,-1,1,-1,1,0,1,-2,1,0,0,0,1,-1,1,-1,0,0,1,-1,1,

%T 0,0,0,0,-1,1,-1,1,0,1,-2,1,0,0,0,1,-1,0,0,1,-1,1,-2,2,-1,0,0,1,-1,1,

%U -1,0,1,0,-1,1,0,0,-1,1,-1,1,-1,1,-1,1,-1,1,0,-1,1,1,-2,2,-2,1,0,1,-2,1,0,0,0,0,0,1,-2,1,0,1,-1,1,-1,0

%N a(1) = 0, then after the first differences of A003434.

%C Also, from a(2) onward the first differences of A049108, and from a(3) onward the first differences of A032358.

%H Antti Karttunen, <a href="/A334196/b334196.txt">Table of n, a(n) for n = 1..65537</a>

%F a(1) = 0; and for n > 1, a(n) = A003434(n) - A003434(n-1).

%t Differences[Array[Length[FixedPointList[EulerPhi, #]] &, 100, 0]] (* _Paolo Xausa_, Aug 18 2024 *)

%o (PARI)

%o A003434(n) = for(k=0, n, n>1 || return(k); n=eulerphi(n));

%o A334196(n) = if(1==n,0,A003434(n)-A003434(n-1));

%Y Cf. A000010, A003434, A032358, A049108, A334195.

%K sign

%O 1,18

%A _Antti Karttunen_, Apr 18 2020