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Search: id:A073477
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| A073477 |
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Least k such that 2^n = k^2-sigma(k)*phi(k). |
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+0
1
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| 2, 4, 8, 16, 32, 12, 20, 256, 44, 1024, 2048, 4096, 8192, 16384, 992, 65536, 724, 262144, 2080, 1048576, 16256, 4194304, 8388608, 16777216, 33554432
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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Sequence is always defined since for s=2^(n+1) 2^n = s^2-sigma(s)*phi(s)
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PROGRAM
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(PARI) a(n)=if(n<0, 0, x=1; while(abs(x^2-sigma(x)*eulerphi(x)-2^n)>0, x++)); x
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CROSSREFS
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Sequence in context: A016020 A119990 A036128 this_sequence A070351 A070350 A070349
Adjacent sequences: A073474 A073475 A073476 this_sequence A073478 A073479 A073480
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KEYWORD
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easy,more,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 26 2002
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EXTENSIONS
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Edited and extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Aug 29 2002
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