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A137510 Irregular 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. 2
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; text; internal format)
OFFSET

1,4

COMMENTS

The length of row n is A264440(n). - Wolfdieter Lang, Jan 16 2016

Row n lists the nontrivial divisors of n, or 0 if there are no such divisors. - Omar E. Pol, Nov 22 2010

LINKS

Table of n, a(n) for n=1..97.

EXAMPLE

From Omar E. Pol, Nov 22 2010: (Start)

The irregular triangle begins:

0;

0;

0;

2;

0;

2, 3;

0;

2, 4;

3;

2, 5;

0,

2, 3, 4, 6;

(End)

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, 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, May 25 2008

MATHEMATICA

Array[Complement[Divisors@ #, {1, #}] &, {42}] /. {} -> {0} // Flatten (* Michael De Vlieger, Jan 16 2016 *)

CROSSREFS

Cf. A070824, A027750, A027751, A264440 (row length). Row sums give A048050.

Sequence in context: A299761 A141099 A127710 * A247303 A067871 A198632

Adjacent sequences:  A137507 A137508 A137509 * A137511 A137512 A137513

KEYWORD

nonn,tabf,easy

AUTHOR

N. J. A. Sloane, May 08 2008

EXTENSIONS

More terms from R. J. Mathar and Emeric Deutsch, May 23 2008

STATUS

approved

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Last modified November 17 00:08 EST 2019. Contains 329209 sequences. (Running on oeis4.)