Primes usually look odd. They’re literally odd , but they typically don’t look like they have a pattern, because a pattern would often imply a way to factor the number.
However, 12345678910987654321 is prime!
from sympy import isprime for b in range(2, 41): n = 0 for i in range(0, b): n += (i+1)*b**i for i in range(b+1, 2*b): n += (2*b-i)*b**i print(b, isprime(n))
 “All primes are odd except 2, which is the oddest of all.” — Concrete Mathematics