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Search: id:A117068
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| A117068 |
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Decimal value of binary number whose n-th 1 is followed by n^2 0's. |
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+0
2
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| 5, 161, 164865, 21609185281, 1450167876173430785, 199309555259989211062227435521, 224402609700066672987369178785813291654447105
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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After a(1) = 5, when is a(n) prime?
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FORMULA
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a(n) = SUM[i=1,n] 2^(n+1).
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EXAMPLE
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a(1) = 5 because 101 (base 2) = 5 (base 10).
a(2) = 161 because 10100001 (base 2) = 161 (base 10).
a(3) = 164865 because 101000010000000001 (base 2) = 164865 (base 10).
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CROSSREFS
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Sequence in context: A088694 A085330 A136368 this_sequence A128068 A129995 A047940
Adjacent sequences: A117065 A117066 A117067 this_sequence A117069 A117070 A117071
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KEYWORD
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base,easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Apr 16 2006
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