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A129138
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a(n) = number of positive divisors of n that are <= phi(n), where phi(n) = A000010(n).
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2
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1, 1, 1, 2, 1, 2, 1, 3, 2, 2, 1, 4, 1, 2, 3, 4, 1, 4, 1, 4, 3, 2, 1, 6, 2, 2, 3, 4, 1, 5, 1, 5, 3, 2, 3, 7, 1, 2, 3, 6, 1, 5, 1, 4, 5, 2, 1, 8, 2, 4, 3, 4, 1, 6, 3, 6, 3, 2, 1, 9, 1, 2, 5, 6, 3, 5, 1, 4, 3, 6, 1, 10, 1, 2, 5, 4, 3, 5, 1, 8, 4, 2, 1, 9, 3, 2, 3, 6, 1, 9, 3, 4, 3, 2, 3, 10, 1, 4, 5, 7, 1, 5, 1, 6
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OFFSET
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1,4
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LINKS
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EXAMPLE
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phi(16) = 8. So a(16) is the number of divisors of 16 which are <= 8. There are 4 such divisors: 1, 2, 4, 8; so a(16) = 4.
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MAPLE
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with(numtheory): a:=proc(n) local div, ct, j: div:=divisors(n): ct:=0: for j from 1 to tau(n) do if div[j]<=phi(n) then ct:=ct+1 else ct:=ct: fi od: ct; end: seq(a(n), n=1..135); # Emeric Deutsch, Mar 31 2007
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MATHEMATICA
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Table[Length[Select[Divisors[n], # <= EulerPhi[n] &]], {n, 104}] (* Jayanta Basu, May 23 2013 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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