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A243997 a(n) = phi(sigma(n) - phi(n) - d(n)), where phi(n) is the Euler totient function, sigma(n) the sum of divisors of n and d(n) the number of divisors of n. 1

%I #5 Jul 12 2014 17:50:46

%S 1,0,0,1,0,2,0,6,2,4,0,6,0,6,4,6,0,18,0,12,8,10,0,20,4,12,6,18,0,24,0,

%T 40,8,16,8,24,0,18,12,20,0,36,0,28,16,22,0,42,4,66,12,32,0,46,12,40,

%U 16,28,0,48,0,30,30,40,16,56,0,40,16,48,0,104,0,36

%N a(n) = phi(sigma(n) - phi(n) - d(n)), where phi(n) is the Euler totient function, sigma(n) the sum of divisors of n and d(n) the number of divisors of n.

%C Subset of A243995.

%C a(p)=0 if p is prime.

%H Paolo P. Lava, <a href="/A243997/b243997.txt">Table of n, a(n) for n = 1..1000</a>

%e sigma(72) = 195, phi(72) = 24, d(72) = 12 and phi(195 - 24 - 12) = 104.

%p with(numtheory): P:=proc(q) local n;

%p for n from 1 to q do print(phi(sigma(n)-phi(n)-tau(n)));

%p od; end: P(100);

%Y Cf. A000005, A000010, A000203, A243995.

%K nonn,easy

%O 1,6

%A _Paolo P. Lava_, Jun 19 2014

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Last modified June 20 22:01 EDT 2024. Contains 373532 sequences. (Running on oeis4.)