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Python

from sympy import isprime, primerange
def fromdigits(digs, base):
    return sum(d*base**i for i, d in enumerate(digs))
def a(n):
    prime_lists, an = [(p, ) for p in primerange(1, n)], 0
    digits = 1
    while len(prime_lists) > 0:
        new_prime_strs = set()
        for p in prime_lists:
            can_extend = False
            for d in range(n):
                c = (d, ) + p
                if isprime(fromdigits(c, n)):
                    can_extend = True
                    new_prime_strs.add(c)
            if not can_extend:
                an += 1
        prime_lists = list(new_prime_strs)
        digits += 1
    return an
print([a(n) for n in range(2, 27)]) # Michael S. Branicky, Dec 11 2022