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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 (list; graph; refs; listen; history; text; internal format)
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
FORMULA
a(n) = n - A047949(n). - Jason Kimberley, Oct 09 2012
MATHEMATICA
a[n_] := For[p = 2, True, p = NextPrime[p], If[PrimeQ[2n-p], Return[p]]];
Table[a[n], {n, 2, 103}] (* Jean-François Alcover, Jul 31 2018 *)
PROG
(PARI) A020481(n) = {local(np); np=1; while(!isprime(2*n-prime(np)), np++); prime(np)} \\ Michael B. Porter, Dec 11 2009
(PARI) A020481(n)=forprime(p=1, n, isprime(2*n-p)&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 A361687 A057957
KEYWORD
nonn
AUTHOR
STATUS
approved

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Last modified July 21 00:40 EDT 2024. Contains 374462 sequences. (Running on oeis4.)