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A175391
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Perfect squares having a square number of divisors.
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2
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1, 36, 100, 196, 225, 256, 441, 484, 676, 1089, 1156, 1225, 1296, 1444, 1521, 2116, 2601, 3025, 3249, 3364, 3844, 4225, 4761, 5476, 5929, 6561, 6724, 7225, 7396, 7569, 8281, 8649, 8836, 9025, 10000, 11236, 12321, 13225, 13924, 14161, 14884, 15129
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OFFSET
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1,2
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COMMENTS
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If m and n are coprime members of the sequence, then m*n is in the sequence.
Includes all numbers of the forms p^(4*i*(i+1)) and p^(2*i)*q^(2*i) where p, q are distinct primes and i is a positive integer. (End)
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LINKS
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FORMULA
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MAPLE
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with(numtheory): a := proc (n) if type(sqrt(tau(n^2)), integer) = true then n^2 else end if end proc: seq(a(n), n = 1 .. 130); # Emeric Deutsch, May 11 2010
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MATHEMATICA
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Select[Range[150], IntegerQ[Sqrt[DivisorSigma[0, #^2]]]&]^2 (* Vincenzo Librandi, Mar 21 2018 *)
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PROG
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(PARI) isok(n) = issquare(n) && issquare(numdiv(n)); \\ Michel Marcus, Mar 21 2018
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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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