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A173581
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Numbers k such that tau(sigma(k)) = rad(k).
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0
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1, 2, 3, 4, 6, 12, 16, 48, 64, 81, 162, 192, 270, 324, 750, 1029, 1296, 1512, 2058, 4096, 4116, 5184, 12288, 16464, 65536, 65856, 196608, 262144, 331776, 786432, 2100000, 4214784, 5308416, 21233664, 67436544, 269746176, 1073741824, 3221225472
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OFFSET
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1,2
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COMMENTS
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rad(n) is the product of the primes dividing n (A007947), tau(n) is the number of divisors of n (A000005), and sigma(n) is the sum of divisor of n (A000203).
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LINKS
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FORMULA
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EXAMPLE
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2 is a member, since sigma(2) = 3, tau(3) = 2 and rad(2) = 2.
65856 is a member, since sigma(65856) = 203200, tau(203200) = 42 and rad(65856) = 42.
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MAPLE
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with(numtheory):for n from 1 to 10000000 do : t1:= ifactors(n)[2] : t2 :=mul(t1[i][1], i=1..nops(t1)):if tau(sigma(n)) = t2 then print (n): else fi: od :
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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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