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Search: id:A053332
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| A053332 |
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a(n) contains n digits (either '4' or '7') and is divisible by 2^n. |
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+0
1
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| 4, 44, 744, 7744, 47744, 447744, 4447744, 44447744, 444447744, 4444447744, 74444447744, 474444447744, 4474444447744, 44474444447744, 444474444447744, 7444474444447744, 77444474444447744, 477444474444447744
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OFFSET
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1,1
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FORMULA
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a(n)=a(n-1)+10^(n-1)*(4+3*[a(n-1)/2^(n-1) mod 2]) i.e. a(n) ends with a(n-1); if (n-1)-th term is divisible by 2^n then n-th term begins with a 4, if not then n-th term begins with a 7.
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EXAMPLE
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a(n)=a(n-1)+10^(n-1)*(4+[a(n-1)/2^(n-1) mod 2]) i.e. a(n) ends with a(n-1); if (n-1)-th term is divisible by 2^n then n-th term begins with a 2, if not then n-th term begins with a 7.
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CROSSREFS
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Cf. A023404, A050621, A050622, A035014.
Sequence in context: A053315 A005721 A056063 this_sequence A088594 A053333 A137783
Adjacent sequences: A053329 A053330 A053331 this_sequence A053333 A053334 A053335
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KEYWORD
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base,nonn
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AUTHOR
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Henry Bottomley (se16(AT)btinternet.com), Mar 06 2000
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