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Search: id:A124143
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| A124143 |
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Perfect powers pp such that sigma(n)=pp for some positive integer n. |
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+0
1
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| 4, 8, 32, 36, 121, 128, 144, 216, 256, 324, 400, 512, 576, 784, 900, 961, 1024, 1296, 1600, 1728, 1764, 1936, 2304, 2704, 2744, 2916, 3136, 3600, 3844, 4096, 4356, 4624, 4900, 5184, 5776, 5832, 6084, 6400, 7056, 7744, 7776, 8000, 8100, 8192, 9216, 9604
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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a(1)=4 since sigma(3)=4=2^2.
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MAPLE
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with(numtheory); egcd := proc(n) local L; if n>1 then L:=ifactors(n)[2]; L:=map(z->z[2], L); return igcd(op(L)) else return 1 fi; end; L:=[]: P:={}: for w to 1 do for n from 1 to 10000 do s:=sigma(n); if egcd(s)>1 then print(n, s, ifactor(s)); L:=[op(L), n]; P:=P union {s}; fi od od; L; P;
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CROSSREFS
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Cf. A001597, A065496.
Adjacent sequences: A124140 A124141 A124142 this_sequence A124144 A124145 A124146
Sequence in context: A080072 A094502 A129195 this_sequence A034041 A050442 A094015
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KEYWORD
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nonn
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AUTHOR
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Walter A. Kehowski (wkehowski(AT)cox.net), Dec 01 2006
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