The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A137510

(Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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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.
(history; published version)

#24 by Jon E. Schoenfield at Sun May 19 02:00:09 EDT 2019

STATUS

editing

approved

#23 by Jon E. Schoenfield at Sun May 19 02:00:06 EDT 2019

MATHEMATICA

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

STATUS

approved

editing

#22 by Michel Marcus at Sat Jan 16 08:07:10 EST 2016

STATUS

reviewed

approved

#21 by Joerg Arndt at Sat Jan 16 07:10:34 EST 2016

STATUS

proposed

reviewed

#20 by Michael De Vlieger at Sat Jan 16 07:04:39 EST 2016

STATUS

editing

proposed

#19 by Michael De Vlieger at Sat Jan 16 07:04:34 EST 2016

MATHEMATICA

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

STATUS

approved

editing

#18 by Wolfdieter Lang at Sat Jan 16 05:46:38 EST 2016

STATUS

editing

approved

#17 by Wolfdieter Lang at Sat Jan 16 05:43:34 EST 2016

NAME

Triangle 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.

COMMENTS

a(n) = 0 if The length of row n is 1 or a primeA264440(n). - _Wolfdieter Lang_, Jan 16 2016

EXAMPLE

Triangle The irregular triangle begins:

CROSSREFS

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

Row sums give A048050.

STATUS

approved

editing

Discussion

Sat Jan 16

05:46

Wolfdieter Lang: The comment line 'a(n) = 0 if n is 1 or a prime.' was wrong:  a(7) = 3. I erased it.

#16 by Jon E. Schoenfield at Sat Oct 03 22:59:27 EDT 2015

STATUS

editing

approved

#15 by Jon E. Schoenfield at Sat Oct 03 22:59:25 EDT 2015

COMMENTS

Row n lists the nontrivial divisors of n, or 0 if there are no such divisors. [From _- _Omar E. Pol_, Nov 22 2010]

EXAMPLE

[Contribution from _From _Omar E. Pol_, Nov 22 2010] : (Start)

Triangle beginbegins:

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

STATUS

approved

editing