Compute OEIS A046253 sequence. For each digit d in a number n, compute d**d; if they sum to n then n is in the sequence.

A046253.py

from functools import lru_cache

@lru_cache
def _powA046253(i, n):
    """Return i**n for two integers i and n. Defines 0**0 to be ZERO."""
    r = i
    while n > 1:
        r *= i
        n -= 1
    return r

def A046253(n):
    """Return True if n is in OEIS A046253 sequence."""

    # https://oeis.org/A046253                                                  
    # Sum the digits of n each raised to itself as a power.                     
    # If that equals n, the number is in A046253.                               
    # NOTE: For this purpose, 0**0 is defined to be zero.                       

    return sum([_powA046253(d, d) for d in [int(a) for a in str(n)]]) == n

def gen_A046253(lim):
    """Generate A046253 numbers < lim."""

    # this is a brute-force search and will be very slow for large lim          
    for i in range(lim):
        if A046253(i):
            yield i