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A189988
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Numbers with prime factorization p^2*q^4.
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10
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144, 324, 400, 784, 1936, 2025, 2500, 2704, 3969, 4624, 5625, 5776, 8464, 9604, 9801, 13456, 13689, 15376, 21609, 21904, 23409, 26896, 29241, 29584, 30625, 35344, 42849, 44944, 55696, 58564, 59536, 60025, 68121, 71824, 75625, 77841
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OFFSET
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1,1
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COMMENTS
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Numbers k such that tau(k^2)/tau(k) = 3 where tau(n) is the number of divisors of n (A000005). - Michel Marcus, Feb 09 2018
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LINKS
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FORMULA
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MATHEMATICA
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f[n_]:=Sort[Last/@FactorInteger[n]]=={2, 4}; Select[Range[150000], f]
Module[{upto=80000}, Select[Union[Flatten[{#[[1]]^2 #[[2]]^4, #[[1]]^4 #[[2]]^2}&/@ Subsets[Prime[Range[Sqrt[upto/16]]], {2}]]], #<=upto&]] (* Harvey P. Dale, Dec 15 2017 *)
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PROG
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(PARI) list(lim)=my(v=List(), t); forprime(p=2, (lim\4)^(1/4), t=p^4; forprime(q=2, sqrt(lim\t), if(p==q, next); listput(v, t*q^2))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jul 20 2011
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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