What is the error in this syntax:

Numbers = {0:'zero' , 1:'one' , 2:'two' , 3:'three' , 4:'four ', 5:'five' , 6:'six' , 7:'seven ', 8:'eight' , 9:'nine'}
a = int( input( 'Enter a number: ')
b =''
for i in a:
        key = int(a)
        c = Numbers[key]
        b = b + ' ' + c
print('Number name = ' ,b)

1. To find the number of elements in a list
2. To find largest and lowest value in a list.
3. To count the occurrences of an element in a list.
4. To find the position of an element in a list.
5. To insert an item at a given position in a list.
6. To add more than one element to the end of the list.
7. To remove and returns the element at given position.