

A020481


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


29



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
a(n) = A171637(n,1).  Reinhard Zumkeller, Mar 03 2014
Conjecture: a(n) ~ O(n^1/2).  Jon Perry, Apr 29 2014


LINKS

H. J. Smith, Table of n, a(n) for n = 2..20000
Index entries for sequences related to Goldbach conjecture


FORMULA

a(n) = n  A047949(n).  Jason Kimberley, Oct 09 2012


MATHEMATICA

a[n_] := For[p = 2, True, p = NextPrime[p], If[PrimeQ[2np], Return[p]]];
Table[a[n], {n, 2, 103}] (* JeanFrançois Alcover, Jul 31 2018 *)


PROG

(PARI) A020481(n) = {local(np); np=1; while(!isprime(2*nprime(np)), np++); prime(np)} \\ Michael B. Porter, Dec 11 2009
(PARI) A020481(n)=forprime(p=1, n, isprime(2*np)&return(p)) \\ M. F. Hasler, Sep 18 2012
(Haskell)
a020481 n = head [p  p < a000040_list, a010051' (2 * n  p) == 1]
 Reinhard Zumkeller, Jul 07 2014, Mar 03 2014


CROSSREFS

Cf. A020482.
Sequence in context: A064338 A197592 A103359 * A066660 A057957 A241686
Adjacent sequences: A020478 A020479 A020480 * A020482 A020483 A020484


KEYWORD

nonn


AUTHOR

David W. Wilson


STATUS

approved



