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A020481
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Least p with p, q both prime, p+q = 2n.
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30
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2, 3, 3, 3, 5, 3, 3, 5, 3, 3, 5, 3, 5, 7, 3, 3, 5, 7, 3, 5, 3, 3, 5, 3, 5, 7, 3, 5, 7, 3, 3, 5, 7, 3, 5, 3, 3, 5, 7, 3, 5, 3, 5, 7, 3, 5, 7, 19, 3, 5, 3, 3, 5, 3, 3, 5, 3, 5, 7, 13, 11, 13, 19, 3, 5, 3, 5, 7, 3, 3, 5, 7, 11, 11, 3, 3, 5, 7, 3, 5, 7, 3, 5, 3, 5, 7, 3, 5, 7, 3, 3, 5, 7, 11, 11, 3, 3, 5, 3, 3, 5, 7
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OFFSET
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2,1
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COMMENTS
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Essentially the same as A002373, which does not have the a(2) term. - T. D. Noe, Sep 24 2007
Conjecture: a(n) ~ O(n^1/2). - Jon Perry, Apr 29 2014
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LINKS
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FORMULA
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MATHEMATICA
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a[n_] := For[p = 2, True, p = NextPrime[p], If[PrimeQ[2n-p], Return[p]]];
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PROG
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(PARI) A020481(n) = {local(np); np=1; while(!isprime(2*n-prime(np)), np++); prime(np)} \\ Michael B. Porter, Dec 11 2009
(Haskell)
a020481 n = head [p | p <- a000040_list, a010051' (2 * n - p) == 1]
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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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