need help with ksh script errors

Shell Programming and Scripting
1 
 
#!/bin/ksh
number1="20"
if [ $1 ]
then
        number1=$1
fi
number2="1"
while [[ $number2 -lt $number1 -o $number2 -eq $number1 ]]
do
        if [[ let "number2 % 3" -eq 0 -a let "number2 % 5" -eq 0 ]]
        then
                print "FizzBuzz"
        elif [[ let "number2 % 3" -eq 0 ]]
                then
                        print "Fizz"
                elif [[ let "number2 % 5" -eq 0 ]]
                        then
                                print "Buzz"
                        else
                                print $number2
        fi
        let "number2++"
done

I am very new to scripting so sorry if this is really messed up. The intention is to use the command line to get a number from the user and then print the numbers 1 through n. only if n is divisble by 3, 5, or both it prints fizz buzz and fizzbuzz instead. also if the command is not enetered the number is set to 20.
With this code i get the error [[: not found and if i only use single "[";s i get test: number2 % 3 unkown operator. please help ive been stuck on this for a while now. thank you. (do i need to set the PATH variable to something specific?) Also this is being done in korn shell

2 
number1="20"
if [ -n "$1" ]
then
    number1=$1
fi

number2=1
while [[ $number2 -le $number1 ]]
do
    if [[ "$number2 % 3" -eq 0 && "$number2 % 5" -eq 0 ]]
    then
        echo "FizzBuzz"
    elif [[ "$number2 % 3" -eq 0 ]]
    then
        echo "Fizz"
    elif [[ "$number2 % 5" -eq 0 ]]
    then
        echo "Buzz"
    else
        echo "$number2"
    fi
    number2=$(($number2 + 1))
done
3

You can try this also. This should work.!

#!/bin/ksh
number1="20"
if [ ${1} ]
then
        number1=${1}
fi
number2="1"
while [[ $number2 -le $number1 ]]
do    
  if [[ $(($number2 % 3 )) -eq "0" && $(($number2 % 5)) -eq "0" ]]; then
    echo "FizzBuzz"
  elif [[ $(($number2 % 3)) -eq "0" ]]
  then
    echo "Fizz"
  elif [[ $(($number2 % 5)) -eq "0" ]]
  then
    echo "Buzz"
  else
    echo "$number2"
  fi
  number2=$(($number2 + 1))
done
4

Using let:

#!/bin/ksh
number=${1:-20}
for (( i=1; i<=$number; i++ )); do
  if   ! let "i % 3 || i % 5 "; then 
    echo "$i FizzBuzz"
  elif ! let "i % 3"; then
    echo "$i Fizz"  
  elif ! let "i % 5"; then
    echo "$i Buzz"  
  fi  
done

or the (( )) version:

#!/bin/ksh
number=${1:-20}
for (( i=1;i<=$number;i++ )); do
  if   ! (( i % 3 || i % 5 )); then 
    echo "$i FizzBuzz"
  elif ! (( i % 3 )); then
    echo "$i Fizz"  
  elif ! (( i % 5 )); then
    echo "$i Buzz"  
  fi  
done

Posix:

number=${1:-20}
i=1
while [ $i -le $number ]; do
  if   [ $(( i % 3 )) -eq 0 ] && [ $(( i % 5 )) -eq 0 ]; then
    echo "$i FizzBuzz"
  elif [ $(( i % 3 )) -eq 0 ]; then
    echo "$i Fizz"  
  elif [ $(( i % 5 )) -eq 0 ]; then
    echo "$i Buzz"  
  fi  
  i=$((i+1))
done