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A074717
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Least k such that floor(2^n/k) is prime.
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1
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1, 2, 3, 3, 6, 9, 11, 11, 7, 9, 5, 10, 19, 11, 5, 10, 9, 11, 22, 35, 39, 9, 5, 10, 20, 27, 11, 19, 9, 18, 36, 25, 29, 27, 5, 10, 20, 40, 61, 13, 21, 42, 29, 27, 39, 9, 17, 29, 58, 49, 27, 25, 50, 11, 22, 44, 39, 11, 22, 44, 29, 58, 116, 53, 19, 38, 76, 152, 237, 139, 5, 10, 20
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OFFSET
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1,2
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LINKS
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FORMULA
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There is probably a constant c such that Sum_{i=1..n} a(i) is asymptotic to c*n^2 (0 < c < 1/2).
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MATHEMATICA
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a[n_] := Module[{k = 1}, While[! PrimeQ @ Floor[2^n/k], k++]; k]; Array[a, 100] (* Amiram Eldar, Aug 31 2020 *)
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PROG
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(PARI) a(n)=if(n<0, 0, k=1; while(isprime(floor(2^n/k)) == 0, k++); k)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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