A073256 -id:A073256 - cp's OEIS frontend

A166362 a(n) = phi(nonprime(n)).

1, 2, 2, 4, 6, 4, 4, 6, 8, 8, 6, 8, 12, 10, 8, 20, 12, 18, 12, 8, 16, 20, 16, 24, 12, 18, 24, 16, 12, 20, 24, 22, 16, 42, 20, 32, 24, 18, 40, 24, 36, 28, 16, 30, 36, 32, 48, 20, 32, 44, 24, 24, 36, 40, 36, 60, 24, 32, 54, 40, 24, 64, 42, 56, 40, 24, 72, 44, 60, 46, 72, 32, 42, 60

Offset: 1

Juri-Stepan Gerasimov, Oct 12 2009

Essentially the same as A073256.

G. C. Greubel, Table of n, a(n) for n = 1..10000

Cf. A000010, A073256, A018252.

Table[EulerPhi[FixedPoint[n + PrimePi@# &, n + PrimePi@n]], {n, 1, 100}] (* G. C. Greubel, May 10 2016 *)

a(n) = A000010(A018252(n)).

Entries checked by R. J. Mathar, May 21 2010

A253473 a(n) = phi(c(n)) - tau(phi(c(n))), where c(n) is the n-th composite number.

Original entry on oeis.org

0, 0, 1, 2, 1, 1, 2, 4, 4, 2, 4, 6, 6, 4, 14, 6, 12, 6, 4, 11, 14, 11, 16, 6, 12, 16, 11, 6, 14, 16, 18, 11, 34, 14, 26, 16, 12, 32, 16, 27, 22, 11, 22, 27, 26, 38, 14, 26, 38, 16, 16, 27, 32, 27, 48, 16, 26, 46, 32, 16, 57, 34, 48, 32, 16, 60, 38, 48, 42, 60

Offset: 1

Carlos Eduardo Olivieri, Jan 02 2015

			For n=1: c(1) = 4. phi(4) = 2. tau(2)= 2, thus a(1) = 2 - 2 = 0.
For n=3: c(3) = 8. phi(8) = 4. tau(4)= 3, thus a(3) = 4 - 3 = 1.
For n=20: c(20) = 32. phi(32) = 16. tau(16) = 5, thus a(20) = 16 - 5 = 11.

Robert Israel, Table of n, a(n) for n = 1..10000
J. Ziegenbalg, Phi, Tau, Sigma in Elementary Number Theory

Cf. A000005, A000010, A002808.

comps:= remove(isprime, [$2..1000]):
map( ((t->t) - numtheory:-tau)@numtheory:-phi, comps); # Robert Israel, Nov 20 2016

Composites := Select[Range[2, 10000], ! PrimeQ[#] &]; Composite[n_] := Last[Take[Composites, n]]; T[n_] := EulerPhi[n]; Table[T[Composite[n]] - DivisorSigma[0, T[Composite[n]]], {n, 200}]
EulerPhi[#]-DivisorSigma[0,EulerPhi[#]]&/@Select[Range[300],CompositeQ] (* Harvey P. Dale, Oct 05 2019 *)

lista(nn) = {forcomposite(n=1, nn, ec = eulerphi(n); print1(ec - numdiv(ec), ", "););} \\ Michel Marcus, Jan 11 2015

a(n) = A049820(A073256(n)). - Michel Marcus, Jan 08 2015

a(n) = A000010(A002808(n)) - A000005(A000010(A002808(n))). - Omar E. Pol, Nov 20 2016

Name clarified by Omar E. Pol, Nov 20 2016

cp's OEIS Frontend

A166362 a(n) = phi(nonprime(n)).

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