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A020481 Least p with p, q both prime, p+q = 2n. 21
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

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

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 A057957 A241686

Adjacent sequences:  A020478 A020479 A020480 * A020482 A020483 A020484

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified December 8 12:55 EST 2016. Contains 278945 sequences.