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A191474
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Smallest prime q such that q + prime(n) is a power of 2.
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2
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2, 5, 3, 549755813881, 5, 3, 47, 13, 41, 3, 97, 2011, 23, 536870869, 17, 11, 5, 3, 61, 953, 439, 433, 173, 167, 31, 67108763, 409, 149, 19, 911, 140737488355201, 16253, 887, 373, 107, 2147483497, 32611, 349, 89, 83, 3917, 331, 16193, 2096959, 59, 313, 33554221
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OFFSET
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1,1
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COMMENTS
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Corresponding exponents of 2: 2, 3, 3, 39, 4, 4, 6, 5, 6, 5, 7, 11, 6, 29, 6, 6, 6, 6, 7, 10, 9, 9, 8, 8, 7, 1, 9, 8, 7, 10, 47, 14, 10, 9, 8, 31, 15, 9, 8, 8, 12, 9, 14, 21, 8, 9, 1, ...
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LINKS
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EXAMPLE
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2 + 2 = 2^2,
3 + 5 = 2^3,
5 + 3 = 2^3,
7 + 549755813881 = 2^39,
11 + 5 = 2^4.
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MAPLE
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f:= proc(n) local p, m, t, q;
p:= ithprime(n);
for t from ilog2(p) do
q:= 2^t - p;
if isprime(q) then return q fi;
od;
end proc:
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MATHEMATICA
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f[p_] := NestWhile[2 # &, 2^Ceiling[Log[2, p]], ! PrimeQ[# - p] &] - p;
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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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