Provided by: libmath-planepath-perl_113-1_all 
NAME
Math::PlanePath::DivisibleColumns -- X divisible by Y in columns
SYNOPSIS
use Math::PlanePath::DivisibleColumns;
my $path = Math::PlanePath::DivisibleColumns->new;
my ($x, $y) = $path->n_to_xy (123);
DESCRIPTION
This path visits points X,Y where X is divisible by Y going by columns from Y=1 to Y<=X.
18 | 57
17 | 51
16 | 49
15 | 44
14 | 40
13 | 36
12 | 34
11 | 28
10 | 26
9 | 22 56
8 | 19 48
7 | 15 39
6 | 13 33 55
5 | 9 25 43
4 | 7 18 32 47
3 | 4 12 21 31 42 54
2 | 2 6 11 17 24 30 38 46 53
1 | 0 1 3 5 8 10 14 16 20 23 27 29 35 37 41 45 50 52
Y=0|
+---------------------------------------------------------
X=0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Starting N=0 at X=1,Y=1 means the values 1,3,5,8,etc horizontally on Y=1 are the sums
i=K
sum numdivisors(i)
i=1
The current implementation is fairly slack and is slow on medium to large N.
Proper Divisors
"divisor_type => 'proper'" gives only proper divisors of X, meaning that Y=X itself is
excluded.
9 | 39
8 | 33
7 | 26
6 | 22 38
5 | 16 29
4 | 11 21 32
3 | 7 13 20 28 37
2 | 3 6 10 15 19 25 31 36
1 | 0 1 2 4 5 8 9 12 14 17 18 23 24 27 30 34 35
Y=0|
+---------------------------------------------------------
X=0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
The pattern is the same, but the X=Y line skipped. The high line going up is at Y=X/2,
when X is even, that being the highest proper divisor.
N Start
The default is to number points starting N=0 as shown above. An optional "n_start" can
give a different start with the same shape, For example to start at 1,
n_start => 1
9 | 23
8 | 20
7 | 16
6 | 14
5 | 10
4 | 8 19
3 | 5 13 22
2 | 3 7 12 18
1 | 1 2 4 6 9 11 15 17 21
Y=0|
+------------------------------
X=0 1 2 3 4 5 6 7 8 9
FUNCTIONS
See "FUNCTIONS" in Math::PlanePath for behaviour common to all path classes.
"$path = Math::PlanePath::DivisibleColumns->new ()"
"$path = Math::PlanePath::DivisibleColumns->new (divisor_type => $str, n_start => $n)"
Create and return a new path object. "divisor_type" (a string) can be
"all" (the default)
"proper"
"($x,$y) = $path->n_to_xy ($n)"
Return the X,Y coordinates of point number $n on the path. Points begin at 0 and if
"$n < 0" then the return is an empty list.
FORMULAS
Rectangle to N Range
The cumulative divisor count up to and including a given X column can be calculated from
the fairly well-known sqrt formula, a sum from 1 to sqrt(X).
S = floor(sqrt(X))
/ i=S \
numdivs cumulative = 2 * | sum floor(X/i) | - S^2
\ i=1 /
This means the N range for 0 to X can be calculated without working out all each column
count up to X. In the current code if column counts have been worked out then they're
used, otherwise this formula.
OEIS
This pattern is in Sloane's Online Encyclopedia of Integer Sequences in the following
forms,
<http://oeis.org/A061017> (etc)
n_start=0 (the default)
A006218 N on Y=1 row, cumulative count of divisors
A077597 N on X=Y diagonal, cumulative count divisors - 1
n_start=1
A061017 X coord, each n appears countdivisors(n) times
A027750 Y coord, list divisors of successive k
A056538 X/Y, divisors high to low
divisor_type=proper (and default n_start=0)
A027751 Y coord divisor_type=proper, divisors of successive n
(extra initial 1)
divisor_type=proper, n_start=2
A208460 X-Y, being X subtract each proper divisor
A208460 has "offset" 2, hence "n_start=2" to match that. The same with all divisors would
simply insert an extra 0 for the difference at X=Y.
SEE ALSO
Math::PlanePath, Math::PlanePath::CoprimeColumns
HOME PAGE
<http://user42.tuxfamily.org/math-planepath/index.html>
LICENSE
Copyright 2011, 2012, 2013 Kevin Ryde
Math-PlanePath is free software; you can redistribute it and/or modify it under the terms
of the GNU General Public License as published by the Free Software Foundation; either
version 3, or (at your option) any later version.
Math-PlanePath is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with Math-
PlanePath. If not, see <http://www.gnu.org/licenses/>.