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1, 4, 12, 24, 50, 72, 126, 176, 252, 320, 462, 552, 754, 896, 1080, 1280, 1632, 1836, 2280, 2560, 2940, 3300, 3956, 4320, 5000, 5512, 6210, 6776, 7830, 8340, 9548, 10368, 11352, 12240, 13440, 14256, 15984, 17100, 18486, 19600, 21730, 22764, 25112
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history;
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internal format)
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OFFSET
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1,2
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COMMENTS
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Also number of reduced fractions with denominators <= n and values between 1/n and n (inclusive). [Reinhard Zumkeller, Jan 15 2009]
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LINKS
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FORMULA
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Equals row sums of triangle A143269.
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EXAMPLE
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a(4) = 24 = sum of row 4 terms of triangle A143269: (4 + 4 + 8 + 8).
a(3) = #{1/3,1/2,2/3,1,4/3,3/2,5/3,2,7/3,5/2,8/3,3} = 12. [Reinhard Zumkeller, Jan 15 2009]
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MATHEMATICA
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Module[{nn=50, ps}, ps=Accumulate[EulerPhi[Range[nn]]]; Times@@@Thread[{Range[nn], ps}]] (* Harvey P. Dale, Jun 04 2023 *)
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PROG
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(Python)
from functools import lru_cache
@lru_cache(maxsize=None)
if n == 0:
return 0
c, j = 0, 2
k1 = n//j
while k1 > 1:
j2 = n//k1 + 1
j, k1 = j2, n//j2
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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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