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A166721
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Squares for which no smaller square has the same number of divisors.
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4
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1, 4, 16, 36, 64, 144, 576, 900, 1024, 1296, 3600, 4096, 5184, 9216, 14400, 32400, 36864, 44100, 46656, 65536, 82944, 129600, 176400, 230400, 262144, 331776, 589824, 705600, 746496, 810000, 921600, 1166400, 1587600, 2073600, 2359296, 2822400, 2985984, 3240000
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OFFSET
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1,2
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COMMENTS
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Numbers k^2 such there is no positive m < k such that A000005(m^2) = A000005(k^2).
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LINKS
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EXAMPLE
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The positive squares begin 1, 4, 9, 16, 25, 36, 49, 64, ..., and their corresponding numbers of divisors are 1, 3, 3, 5, 3, 9, 3, 7, ...; thus, a(1)=1, a(2)=4, 9 is not a term (it has the same number of divisors as does 4; the same is true of 25, 49, etc.), a(3)=16, a(4)=36, a(5)=64, ... - Jon E. Schoenfield, Mar 03 2018
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MATHEMATICA
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Sort[Module[{nn=2000, tbl}, tbl=Table[{n^2, DivisorSigma[0, n^2]}, {n, nn}]; Table[ SelectFirst[ tbl, #[[2]]==k&], {k, nn}]][[All, 1]]/."NotFound"->Nothing] (* Harvey P. Dale, Jun 06 2022 *)
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PROG
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(PARI) lista(nn) = {v = []; for (n=1, nn, d = numdiv(n^2); if (! vecsearch(v, d), print1(n^2, ", "); v = Set(concat(v, d))); ); } \\ Michel Marcus, Mar 04 2018
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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Alexander Isaev (i2357(AT)mail.ru), Oct 20 2009
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EXTENSIONS
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STATUS
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approved
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