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A073046 Write 2*n = p+q (p,q prime), p*q minimal; then a(n) = p*q. 5
4, 9, 15, 21, 35, 33, 39, 65, 51, 57, 95, 69, 115, 161, 87, 93, 155, 217, 111, 185, 123, 129, 215, 141, 235, 329, 159, 265, 371, 177, 183, 305, 427, 201, 335, 213, 219, 365, 511, 237, 395, 249, 415, 581, 267, 445, 623, 1501, 291, 485, 303, 309, 515, 321, 327 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

Least semiprime whose sum of prime factors equals 2*n.

Assuming Goldbach's conjecture, a(n) exists for all n >= 2. - David James Sycamore, Jan 08 2019

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 2..10000

FORMULA

For all n except 3, a(n) = A288814(2*n). - David James Sycamore, Jan 08 2019

EXAMPLE

n=13: 2n=26; 26 = 23 + 3 = 19 + 7 = 13 + 13; 23*3 = minimal => p*q = 23*3 = 69.

PROG

(Haskell)

a073046 n = head $ dropWhile (== 0) $

                   zipWith (*) prims $ map (a061397 . (2*n -)) prims

   where prims = takeWhile (<= n) a000040_list

-- Reinhard Zumkeller, Aug 28 2011

CROSSREFS

Cf. A000040, A061397.

Cf. A102084, A193315, A288814.

Sequence in context: A103395 A103393 A103392 * A066495 A313298 A313299

Adjacent sequences:  A073043 A073044 A073045 * A073047 A073048 A073049

KEYWORD

nonn

AUTHOR

Werner D. Sand, Aug 31 2002

EXTENSIONS

Corrected by Ray Chandler, Jun 11 2005

STATUS

approved

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Last modified March 20 07:27 EDT 2019. Contains 321345 sequences. (Running on oeis4.)