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A133830
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Least positive number k<n such that the binary trinomial 1 + 2^n + 2^k is prime, or 0 if there is no such k.
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1
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1, 1, 1, 2, 1, 1, 0, 3, 3, 2, 1, 4, 5, 1, 1, 11, 1, 6, 5, 4, 7, 3, 9, 0, 17, 15, 1, 15, 1, 6, 0, 4, 9, 14, 13, 3, 11, 25, 0, 6, 7, 0, 17, 7, 15, 2, 0, 30, 23, 6, 21, 2, 33, 1, 0, 3, 0, 14, 5, 6, 21, 19, 0, 30, 3, 1, 5, 34, 19, 26, 17, 19, 17, 5, 33, 15, 23, 27, 33, 4, 3, 26, 1, 39, 35, 19, 9, 18
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OFFSET
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2,4
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COMMENTS
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Sequence A081504 gives the n such that a(n)=0. For those n, A133831(n) gives the k>n for which the binary trinomial is prime.
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LINKS
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MATHEMATICA
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Table[s=1+2^n; k=1; While[k<n && !PrimeQ[s+2^k], k++ ]; If[k==n, 0, k], {n, 100}]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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