Trying to find the next prime number

[Pedroski55]

Maths is definitely not my thing, but I tried like this:

Apart from 2, all prime numbers are odd.
Numbers ending in 0 or 5 are divisible by 5.
Numbers whose cross-sum is divisible by 3 are divisible by 3
11 is a strange number with weird properties, but that's another story!

A function to find prime numbers. I never played with prime numbers before, I hope this works!

def isPrime(anum):
    noP = {'0', '2', '4', '5', '6', '8'}
    P = {1, 2, 3, 5, 7}
    word = str(anum)
    if anum in P:
        #print(anum, 'is a prime number ... ')
        return True
    elif word[-1] in noP:
        #print(anum, 'is not a prime number.')
        return False
    sum_num = 0
    for w in word:
        sum_num = sum_num + int(w)
    if sum_num % 3 == 0:
        #print('The sum of', anum, 'is divisible by 3 so', anum, 'is not a prime number.')
        return False
    others = {7, 9}
    for n in others:
        if anum % n == 0:
            #print(anum, ' is divisible by', n, 'is not a prime number.')
            return False
    print('Can not find a factor for', anum, 'so it must be prime ... ')
    return True

You can get prime numbers using this:

for num in range(3, 2004, 2):
    if isPrime(num):
        print('*****************')
        print('The next prime number is', num)
        print('*****************')

For a given number, find the next prime number:

start = int(input('Enter a number ... '))
if not isPrime(start + 1):
    count = 1
    while not isPrime(start+ count):
        isPrime(start + count)
        count +=1
else:
    print('The next prime number is', start + count)

Check if a number is prime:

for n in range(1,2004):
    if 2003 % n == 0:
        print(n)

But I don't know if this uses too much time!