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Search: id:A054987
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| A054987 |
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Smallest composite x such that Sigma[x+2^n]=Sigma[x]+2^n; n>2. |
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+0
5
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| 434, 305635357, 27, 39, 106645, 69, 2275, 63, 6475, 249, 7735, 3703, 10803, 16383, 58869, 51181, 87951, 1695, 9579, 105237, 98829, 1143369, 789609, 11625, 14038691, 178975, 48627929, 1881333, 402373721, 2667945, 82915599, 353195221, 70106601
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The sequence is initiated by smallest of A015915. Special primes of A023202, A049488-A049491 also satisfy the Sigma[p+2^w]=Sigma[p]+2^w relation
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EXAMPLE
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For the term 69: Sigma[69+2^6] = Sigma[133] = 1+7+19+133 = Sigma[69]+64 = (1+3+23+69)+64 = 160.
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MATHEMATICA
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Table[ Select[ Range[ 1, 110000 ], Equal[ EulerPhi[ #+2^k ]-EulerPhi[ # ]-2^k, 0 ] &&!PrimeQ[ # ]& ], {k, 1, 22} ]
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CROSSREFS
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Cf. A049488-A049491, A001359, A054799, A015913, A015915, A023200, A023202, A054905.
Sequence in context: A108785 A050507 A145318 this_sequence A054905 A160353 A124043
Adjacent sequences: A054984 A054985 A054986 this_sequence A054988 A054989 A054990
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), May 29 2000
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EXTENSIONS
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More terms from Labos E. (labos(AT)ana.sote.hu), Aug 14 2003
a(21) corrected and a(27)-a(33) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Nov 30 2008
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