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A063755
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Squares k which are divisible by phi(k).
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1
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1, 4, 16, 36, 64, 144, 256, 324, 576, 1024, 1296, 2304, 2916, 4096, 5184, 9216, 11664, 16384, 20736, 26244, 36864, 46656, 65536, 82944, 104976, 147456, 186624, 236196, 262144, 331776, 419904, 589824, 746496, 944784, 1048576, 1327104
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OFFSET
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1,2
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LINKS
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FORMULA
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Sum_{n>=1) 1/a(n) = 11/8. (End)
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MATHEMATICA
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Select[ Range[ 1, 2000 ], Mod[ #^2, EulerPhi[ #^2 ] ]==0& ]^2
Select[Range[2000]^2, Divisible[#, EulerPhi[#]]&] (* Harvey P. Dale, Dec 11 2010 *)
Join[{1}, Sort @ Flatten @ Table[2^i*3^j, {i, 2, Log2[m], 2}, {j, 0, Log[3, m/2^i], 2}]] (* Amiram Eldar, Oct 29 2020 *)
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PROG
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(PARI) j=[]; for(n=1, 2000, if(Mod(n^2, eulerphi(n^2))==0, j=concat(j, n^2))); j
(PARI) { n=0; for (m=1, 10^9, s=m^2; if (s%eulerphi(s)==0, write("b063755.txt", n++, " ", s); if (n==160, break)) ) } \\ Harry J. Smith, Aug 29 2009
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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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