# Copyright 2010, 2011, 2012 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 .
package Math::NumSeq::SafePrimes;
use 5.004;
use strict;
use vars '$VERSION', '@ISA';
$VERSION = 37;
use Math::NumSeq::Primes;
@ISA = ('Math::NumSeq::Primes');
# uncomment this to run the ### lines
#use Smart::Comments;
use constant description => Math::NumSeq::__('The safe primes 5,7,11,23,47, being primes where (P-1)/2 is also prime (those are the Sophie Germain primes).');
use constant values_min => 5;
use constant characteristic_increasing => 1;
use constant oeis_anum => 'A005385';
sub rewind {
my ($self) = @_;
$self->SUPER::rewind;
$self->{'safe_i'} = 0;
$self->{'safe_bseq'} = Math::NumSeq::Primes->new;
}
sub next {
my ($self) = @_;
my $bseq = $self->{'safe_bseq'};
my $behind = 0;
for (;;) {
(undef, my $prime) = $self->SUPER::next
or return;
my $target = ($prime-1)/2;
while ($behind < $target) {
(undef, $behind) = $bseq->next
or return;
}
if ($behind == $target) {
return (++$self->{'safe_i'}, $prime);
}
}
}
sub pred {
my ($self, $value) = @_;
return (($value & 1)
&& $self->SUPER::pred ($value)
&& $self->SUPER::pred (($value-1)/2));
}
1;
__END__