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A081308
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Number of ways to write n as sum of a prime and an 3-smooth number.
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6
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0, 0, 1, 2, 2, 3, 2, 3, 3, 2, 4, 2, 3, 4, 4, 2, 3, 2, 5, 4, 5, 2, 5, 1, 5, 3, 4, 1, 6, 2, 5, 4, 3, 3, 7, 0, 5, 4, 5, 3, 5, 1, 6, 3, 5, 3, 6, 1, 7, 4, 4, 1, 6, 1, 8, 4, 3, 1, 7, 1, 7, 3, 4, 2, 8, 1, 7, 3, 5, 3, 7, 1, 6, 4, 7, 2, 10, 0, 8, 3, 3, 2, 9, 2, 9, 3, 4, 3, 6, 1, 9, 3, 3, 2, 9, 0, 5, 5, 4, 3, 8, 1, 7, 3, 6
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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COMMENTS
| Asymptotically, for n coprime to 6, a(n) ~ C*n on the average, with C=3/(2*log(2)*log(3))~1.969796..., see the link. - M. F. Hasler, Oct 21 2011
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LINKS
| Mark Underwood, another goldbachian theme, Mar. 16, 2009 and follow-up on Oct. 21, 2011.
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EXAMPLE
| a(12)=2: 12=11+1=3+3^2; a(13)=3: 13=11+2=7+2*3=5+2^3.
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PROG
| (PARI) A081308(n)=my(L2=log(2)); sum(e3=0, log(n+.5)\log(3), sum(e2=0, log(n\3^e3)\L2, isprime(n-(3^e3)<<e2))) \\ - M. F. Hasler, Oct 21 2011
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CROSSREFS
| Cf. A081310, A081311, A081309, A000040, A003586.
Sequence in context: A031266 A109301 A107573 * A070210 A197775 A100198
Adjacent sequences: A081305 A081306 A081307 * A081309 A081310 A081311
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KEYWORD
| nonn
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AUTHOR
| Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Mar 17 2003
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