

A020481


Least p with p, q both prime, p+q = 2n.


30



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

2,1


COMMENTS

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


LINKS



FORMULA



MATHEMATICA

a[n_] := For[p = 2, True, p = NextPrime[p], If[PrimeQ[2np], Return[p]]];


PROG

(PARI) A020481(n) = {local(np); np=1; while(!isprime(2*nprime(np)), np++); prime(np)} \\ Michael B. Porter, Dec 11 2009
(Haskell)
a020481 n = head [p  p < a000040_list, a010051' (2 * n  p) == 1]


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



