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Search: id:A088434
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| A088434 |
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Number of ways to write n as n = u*v*w with 1<=u<v<w. |
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+0
6
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| 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 1, 1, 0, 2, 0, 2, 1, 1, 0, 4, 0, 1, 1, 2, 0, 4, 0, 2, 1, 1, 1, 4, 0, 1, 1, 4, 0, 4, 0, 2, 2, 1, 0, 6, 0, 2, 1, 2, 0, 4, 1, 4, 1, 1, 0, 8, 0, 1, 2, 3, 1, 4, 0, 2, 1, 4, 0, 8, 0, 1, 2, 2, 1, 4, 0, 6, 1, 1, 0, 8, 1, 1, 1, 4, 0, 8, 1, 2, 1, 1, 1, 9, 0, 2, 2, 4, 0, 4
(list; graph; listen)
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OFFSET
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1,12
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COMMENT
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a(n)=0 iff n=1 or n prime or n prime^2: a(A000430(n))=0.
The integers a(n)+1 equal A045778(n) for n<120 and differ at all n that admit factorization into 4 or more distinct factors, the smallest ones being n=120=2*3*4*5, n=144=2*3*4*6, n=168=2*3*4*7, n=180=2*3*5*6, ..., later continueing n=312=2*3*4*13, n=320=2*4*5*8, n=324=2*3*6*9, n=330=2*3*5*11,... Coincidentally, A068350(5) to A068350(19) start this list. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 19 2007
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EXAMPLE
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n=12: (1,2,6), (1,3,4): therefore a(12)=2;
n=18: (1,2,9), (1,3,6): therefore a(18)=2.
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CROSSREFS
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Cf. A034836, A088432, A088433.
Sequence in context: A084114 A110475 A086971 this_sequence A034178 A131341 A074169
Adjacent sequences: A088431 A088432 A088433 this_sequence A088435 A088436 A088437
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Oct 01 2003
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