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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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1
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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EXAMPLE
| 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
| 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 (deutsch(AT)duke.poly.edu), Mar 31 2007
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CROSSREFS
| Cf. A129139, A126131, A074919.
Sequence in context: A033273 A034836 A001055 * A112970 A112971 A050379
Adjacent sequences: A129135 A129136 A129137 * A129139 A129140 A129141
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet, Mar 30 2007
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 31 2007
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