A330739 - OEIS

%I #7 Jan 11 2020 21:50:04

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

%T 2,3,1,3,4,2,1,5,1,2,1,2,1,3,1,5,2,2,1,2,2,2,3,3,1,6,1,4,2,1,3,2,1,4,

%U 1,7,1,1,1,4,5,1,2,8,1,3,1,3,1,5,1,3,2,2,1,3,2,2,4,2,3,1,1,6,2,4,1,4,1,1,7

%N Number of values of k, 1 <= k <= n, with A047994(k) = A047994(n), where A047994 is unitary totient function uphi(n).

%C Ordinal transform of A047994.

%H Antti Karttunen, <a href="/A330739/b330739.txt">Table of n, a(n) for n = 1..65537</a>

%o (PARI)

%o up_to = 65537;

%o ordinal_transform(invec) = { my(om = Map(), outvec = vector(length(invec)), pt); for(i=1, length(invec), if(mapisdefined(om,invec[i]), pt = mapget(om, invec[i]), pt = 0); outvec[i] = (1+pt); mapput(om,invec[i],(1+pt))); outvec; };

%o A047994(n) = { my(f=factor(n)~); prod(i=1, #f, (f[1, i]^f[2, i])-1); };

%o v330739 = ordinal_transform(vector(up_to, n, A047994(n)));

%o A330739(n) = v330739[n];

%Y Cf. A047994.

%Y Cf. also A081373 (ordinal transform of Euler totient function phi), A331177.

%K nonn

%O 1,2

%A _Antti Karttunen_, Jan 11 2020