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A137510
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Triangle read by rows in which row n lists the divisors of n in the range 1 < d < n; or 0 if there are no such divisors.
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0
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0, 0, 0, 2, 0, 2, 3, 0, 2, 4, 3, 2, 5, 0, 2, 3, 4, 6, 0, 2, 7, 3, 5, 2, 4, 8, 0, 2, 3, 6, 9, 0, 2, 4, 5, 10, 3, 7, 2, 11, 0, 2, 3, 4, 6, 8, 12, 5, 2, 13, 3, 9, 2, 4, 7, 14, 0, 2, 3, 5, 6, 10, 15, 0, 2, 4, 8, 16, 3, 11, 2, 17, 5, 7, 2, 3, 4, 6, 9, 12, 18, 0, 2, 19, 3, 13, 2, 4, 5, 8, 10, 20, 0, 2, 3, 6, 7
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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COMMENTS
| a(n) = 0 if n is 1 or a prime.
Row n lists the nontrivial divisors of n, or 0 if there are no such divisors. [From Omar E. Pol (info(AT)polprimos.com), Nov 22 2010]
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EXAMPLE
| [Contribution from Omar E. Pol (info(AT)polprimos.com), Nov 22 2010] (Start)
Triangle begin:
0;
0;
0;
2;
0;
2, 3;
0;
2, 4;
3;
2, 5;
0,
2, 3, 4, 6;
(End)
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MAPLE
| for n from 1 to 80 do if isprime(n) or n = 1 then printf("0, ") ; else dvs := sort(convert(numtheory[divisors](n) minus {1, n}, list) ) ; for d in dvs do printf("%d, ", d) ; od: fi ; od: - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 23 2008
with(numtheory): A:=proc (n) local div: div:=divisors(n): `minus`(div, {div[tau(n)], div[1]}) end proc: for n to 35 do A(n) end do: a:=proc (n) if A(n)={} then 0 else seq(A(n)[j], j=1..tau(n)-2) end if end proc: for n to 35 do a(n) end do; # yields sequence in triangular form - Emeric Deutsch (deutsch(AT)duke.poly.edu), May 25 2008
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CROSSREFS
| Cf. A070824, A027750, A027751.
Row sums give A048050.
Sequence in context: A111565 A141099 A127710 * A067871 A198632 A060155
Adjacent sequences: A137507 A137508 A137509 * A137511 A137512 A137513
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KEYWORD
| nonn,tabf,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), May 08 2008
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EXTENSIONS
| More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl) and Emeric Deutsch (deutsch(AT)duke.poly.edu), May 23 2008
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