# Copyright 2011, 2012, 2013, 2014 Kevin Ryde
# This file is part of Math-NumSeq.
#
# Math-NumSeq 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-NumSeq 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-NumSeq. If not, see <http://www.gnu.org/licenses/>.
package Math::NumSeq::HappyNumbers;
use 5.004;
use strict;
use List::Util 'sum';
use vars '$VERSION', '@ISA';
$VERSION = 72;
use Math::NumSeq;
use Math::NumSeq::Base::IteratePred;
@ISA = ('Math::NumSeq::Base::IteratePred',
'Math::NumSeq');
*_is_infinite = \&Math::NumSeq::_is_infinite;
use Math::NumSeq::Repdigits;
*_digit_split_lowtohigh = \&Math::NumSeq::Repdigits::_digit_split_lowtohigh;
# uncomment this to run the ### lines
# use Smart::Comments;
# use constant name => Math::NumSeq::__('Happy Numbers');
use constant description => Math::NumSeq::__('Happy numbers 1,7,10,13,19,23,etc, reaching 1 under iterating sum of squares of digits.');
use constant default_i_start => 1;
use constant values_min => 1;
use Math::NumSeq::Base::Digits
'parameter_info_array'; # radix parameter
#------------------------------------------------------------------------------
# cf A035497 happy primes, happy numbers which are prime
# A003621 how many steps to reach 1 or 4
# A090425 how many steps for just the happy numbers
# A031176 period of final cycle, being 1 or 8 in decimal
#
# A000216 start 2 the cycle 4,16,37,58,89,145,42,20
# A000218 start 3
# A080709 start 4
# A000221 start 5
# A008460 start 6
# A008462 start 8
# A008463 start 9
# A139566 start 15
# A122065 start 74169
#
my @oeis_anum;
$oeis_anum[2] = 'A000027'; # 1,2,3,4, everything happy in base 2
# OEIS-Other: A000027 radix=2
$oeis_anum[4] = 'A000027'; # 1,2,3,4, everything happy in base 4
# OEIS-Other: A000027 radix=4
$oeis_anum[10] = 'A007770';
# OEIS-Catalogue: A007770 radix=10
sub oeis_anum {
my ($self) = @_;
return $oeis_anum[$self->{'radix'}];
}
#------------------------------------------------------------------------------
sub pred {
my ($self, $value) = @_;
### HappyNumbers pred(): $value
if ($value <= 0
|| $value != int($value)
|| _is_infinite($value)) {
return 0;
}
my $radix = $self->{'radix'};
my %seen;
for (;;) {
### $value
if ($value == 1) {
return 1;
}
if ($seen{$value}) {
return 0; # inf loop
}
$seen{$value} = 1;
$value = _sum_of_squares_of_digits($value,$radix);
}
}
sub _sum_of_squares_of_digits {
my ($n, $radix) = @_;
return sum (map {$_ * $_} _digit_split_lowtohigh($n,$radix));
}
1;
__END__
=for stopwords Ryde Math-NumSeq ie
=head1 NAME
Math::NumSeq::HappyNumbers -- reaching 1 under repeated sum of squares of digits
=head1 SYNOPSIS
use Math::NumSeq::HappyNumbers;
my $seq = Math::NumSeq::HappyNumbers->new;
my ($i, $value) = $seq->next;
=head1 DESCRIPTION
This sequence is the happy numbers which are the numbers eventually reaching
1 on repeatedly taking the sum of the squares of the digits.
1, 7, 10, 13, 19, 23, ...
starting i=1
For example 23 is a happy number because the sum of squares of its digits
(ie. 2 and 3) is 2*2+3*3=13, then the same sum of squares again 1*1+3*3=10,
then 1*1+0*0=1 reaches 1.
In decimal it can be shown that for a non-zero starting point this procedure
always reaches either 1 or the cycle 4,16,37,58,89,145,42,20. The values
which reach 1 are called happy numbers.
An optional C<radix> parameter can select a base other than decimal. Base 2
and base 4 are not very interesting since for them every number except 0 is
happy.
=head1 FUNCTIONS
See L<Math::NumSeq/FUNCTIONS> for behaviour common to all sequence classes.
=over 4
=item C<$seq = Math::NumSeq::HappyNumbers-E<gt>new ()>
=item C<$seq = Math::NumSeq::HappyNumbers-E<gt>new (radix =E<gt> $r)>
Create and return a new sequence object.
=item C<$bool = $seq-E<gt>pred($value)>
Return true if C<$value> is a happy number, meaning repeated sum of squares
of its digits reaches 1.
=back
=head1 SEE ALSO
L<Math::NumSeq>,
L<Math::NumSeq::HappySteps>,
L<Math::NumSeq::DigitSum>
=head1 HOME PAGE
L<http://user42.tuxfamily.org/math-numseq/index.html>
=head1 LICENSE
Copyright 2011, 2012, 2013, 2014 Kevin Ryde
Math-NumSeq 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-NumSeq 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-NumSeq. If not, see <http://www.gnu.org/licenses/>.
=cut