sub Check_ABN {
	my $number = shift ;
	my $abn_invalid = 0 ;
	my $sum = 0 ;
	$number =~ s/\ //g ;
	unless (length($number) eq 11) {
		$abn_invalid = 1 ;
		return $abn_invalid ;
	}
	
	$sum += (substr($number,0,1)-1)*10 ;
	$sum += substr($number,1,1)*1 ;
	$sum += substr($number,2,1)*3 ;
	$sum += substr($number,3,1)*5 ;
	$sum += substr($number,4,1)*7 ;
	$sum += substr($number,5,1)*9 ;
	$sum += substr($number,6,1)*11 ;
	$sum += substr($number,7,1)*13 ;
	$sum += substr($number,8,1)*15 ;
	$sum += substr($number,9,1)*17 ;
	$sum += substr($number,10,1)*19 ;
	if ($sum % 89 eq 0) {
		return $abn_invalid ;
	} else {
		$abn_error = 1 ;
		return $abn_invalid ;
	}
	# see https://abr.business.gov.au/Help/AbnFormat
}