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A093312
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Least k such that (2n + 2k) + 1 and (2n*2k) + 1 are both primes.
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2
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1, 9, 3, 1, 3, 3, 1, 3, 2, 1, 9, 2, 1, 6, 3, 4, 6, 8, 10, 3, 5, 1, 3, 2, 1, 3, 12, 1, 15, 5, 13, 9, 3, 1, 18, 3, 4, 3, 2, 4, 33, 2, 1, 12, 3, 7, 6, 3, 1, 3, 2, 16, 15, 2, 13, 9, 17, 25, 15, 5, 4, 6, 26, 1, 9, 8, 1, 30, 5, 16, 3, 2, 1, 15, 6, 7, 12, 3, 7, 15, 5, 7, 3, 2, 4, 3, 12, 1, 6, 5, 7, 36, 3, 22
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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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EXAMPLE
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a(4) = 1, 8 + 2*2 + 1 = 11 and 8*2*2 + 1 = 17 are both prime.
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MAPLE
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f:= proc(n) local k;
for k from 1 do if isprime(2*n+2*k+1) and isprime(4*n*k+1) then return k fi od
end proc:
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MATHEMATICA
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f[n_] := Block[{k = 1}, While[ !PrimeQ[2n + 2k + 1] || ! PrimeQ[2n*2k + 1], k++ ]; k]; Table[ f[n], {n, 95}] (* Robert G. Wilson v, Apr 24 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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