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A027751
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Triangle read by rows in which row n lists the proper divisors of n (those divisors of n which are < n), with the first row {1} by convention.
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5
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1, 1, 1, 1, 2, 1, 1, 2, 3, 1, 1, 2, 4, 1, 3, 1, 2, 5, 1, 1, 2, 3, 4, 6, 1, 1, 2, 7, 1, 3, 5, 1, 2, 4, 8, 1, 1, 2, 3, 6, 9, 1, 1, 2, 4, 5, 10, 1, 3, 7, 1, 2, 11, 1, 1, 2, 3, 4, 6, 8, 12, 1, 5, 1, 2, 13, 1, 3, 9, 1, 2, 4, 7, 14, 1, 1, 2, 3, 5, 6, 10, 15, 1, 1, 2, 4, 8, 16, 1, 3, 11, 1, 2, 17, 1, 5, 7, 1, 2, 3, 4, 6, 9, 12, 18
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,5
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COMMENTS
| Or, take the list 1,2,3,4,... of natural numbers (A000027) and replace each number by its proper divisors.
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EXAMPLE
| Triangle begins:
1,
1,
1,
1, 2,
1,
1, 2, 3,
1,
1, 2, 4,
1, 3,
1, 2, 5,
1,
1, 2, 3, 4, 6,
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CROSSREFS
| Cf. A027750, A032741, A001065, A000005.
Row sums give A173455. [From Omar E. Pol (info(AT)polprimos.com), Nov 23 2010]
Sequence in context: A144328 A140207 A104763 * A181322 A004070 A180562
Adjacent sequences: A027748 A027749 A027750 * A027752 A027753 A027754
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KEYWORD
| nonn,easy,tabf
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Patrick De Geest (pdg(AT)worldofnumbers.com), May 15 1998.
Example edited by Omar E. Pol (info(AT)polprimos.com), Nov 23 2010
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