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A092507
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(Smallest prime >= 2^n) + (largest prime <= 2^n).
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1
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2, 4, 8, 18, 30, 68, 128, 258, 508, 1030, 2052, 4092, 8192, 16400, 32792, 65520, 131058, 262172, 524286, 1048596, 2097156, 4194312, 8388620, 16777210, 33554472, 67108860, 134217738, 268435446, 536870858, 1073741832, 2147483616
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OFFSET
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0,1
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COMMENTS
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For n=0 we just take a(0)=2, the least prime >= 2^0, as there is no prime <= 2^0. - Robert Israel, Nov 01 2018
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LINKS
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FORMULA
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MAPLE
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[2, seq( (nextprime(2^x-1)+prevprime(2^x+1)), x=1..20)]; # Corrected by Robert Israel, Nov 01 2018
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MATHEMATICA
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PrevPrim[n_] := Block[{k = n - 1}, While[ !PrimeQ[k], k-- ]; k]; NextPrim[n_] := Block[{k = n + 1}, While[ !PrimeQ[k], k++ ]; k]; Table[PrevPrim[2^n+1] + NextPrim[2^n-1], {n, 31}] (* Robert G. Wilson v, Apr 14 2004 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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