login
A073256
a(n) = phi(n-th composite number).
3
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
1,1
LINKS
FORMULA
a(n) = A000010(A002808(n)).
EXAMPLE
100th composite is 133; phi(133) = 108 = a(100).
MATHEMATICA
c[x_] := FixedPoint[x+PrimePi[ # ]+1&, x] Table[EulerPhi[c[w], {w, 1, 128}]
With[{nn=100}, EulerPhi[#]&/@Complement[Range[2, nn], Prime[Range[ PrimePi[ nn]]]]] (* Harvey P. Dale, Apr 28 2014 *)
EulerPhi[Select[Range[100], CompositeQ]] (* Harvey P. Dale, Jul 05 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jul 22 2002
STATUS
approved