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A081309 Smallest prime p such that n-p is an 3-smooth number, a(n)=0 if no such prime exists. 2
0, 0, 2, 2, 2, 2, 3, 2, 3, 2, 2, 3, 5, 2, 3, 7, 5, 2, 3, 2, 3, 13, 5, 23, 7, 2, 3, 19, 2, 3, 7, 5, 17, 2, 3, 0, 5, 2, 3, 13, 5, 41, 7, 17, 13, 19, 11, 47, 13, 2, 3, 43, 5, 53, 7, 2, 3, 31, 5, 59, 7, 53, 31, 37, 11, 2, 3, 41, 5, 43, 7, 71, 19, 2, 3, 67, 5, 0, 7, 53, 17, 73, 2, 3, 13, 5, 23, 7, 17, 89 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(n)=0 iff A081308(n)=0.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

EXAMPLE

a(25)=7: 25=7+2*3^2.

PROG

(Haskell)

a081309 n | null ps   = 0

          | otherwise = head ps

          where ps = [p | p <- takeWhile (< n) a000040_list,

                          a065333 (n - p) == 1]

-- Reinhard Zumkeller, Jul 04 2012

CROSSREFS

Cf. A081310, A081311, A081309, A000040, A003586.

Cf. A065333.

Sequence in context: A165035 A236531 A217403 * A010553 A262095 A163374

Adjacent sequences:  A081306 A081307 A081308 * A081310 A081311 A081312

KEYWORD

nonn,look

AUTHOR

Reinhard Zumkeller, Mar 17 2003

STATUS

approved

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Last modified May 27 06:24 EDT 2019. Contains 323599 sequences. (Running on oeis4.)