# カタラン数 Catalan Number
# 引数 整数 ($n)
# 戻り値 カタラン数 ($CatalanNumber)
sub CATALANNUMBER{
	my ($n) = @_;
	my $CatalanNumber = 0;
	my @Catalan = (0);
	my $Combination = 0;
	my $BinomialCoefficient = 0;
	my $N = int($n);
	
	# 整数の確認
	if($N < 1){
		return 0;
	}
	
	# 計算
	for(my $i = 0; $i <= 1; $i++){
		$Combination = $N * 2;
		$BinomialCoefficient = 1;

		for(my $j = 1; $j <= ($N - $i); $j++){
			# 二項係数 Binomial Coefficient
			$Combination = $Combination / $j;
			$BinomialCoefficient = $Combination;
			$Combination = $Combination * (($N * 2) - $j);
		}

		$Catalan[$i] = $BinomialCoefficient;
	}
	
	# カタラン数 Catalan Number
	$CatalanNumber = $Catalan[0] - $Catalan[1];

	return $CatalanNumber;
}