A379776 a(n) = position of prime(n) in A379775, or a(n) = -1 if prime(n) is not in A379775.

1, 2, 3, 6, 5, 7, 4, 12, 25, 11, 20, 13, 40, 33, 43, 45, 27, 21, 44, 42, 14, 48, 71, 26, 8, 72, 64, 41, 112, 23, 116, 82, 111, 46, 62, 53, 49, 152, 80, 75, 37, 262, 122, 9, 99, 93, 38, 115, 52, 343, 28, 286, 22, 162, 104, 274, 36, 87, 47, 70, 171, 79, 18, 140

Offset: 1

Author

Robert C. Lyons, Jan 02 2025

Keywords

• nonn
• easy

Links

• Robert C. Lyons, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A379775.

Programs

Python

from sympy import prime, primefactors, primepi
def get_a379776(a379775_indices):
    a379776 = []
    count = 1
    while True:
        p = prime(count)
        if p not in a379775_indices:
            break
        a379776.append(a379775_indices[p])
        count += 1
    return a379776
a379775 = [2]
a379775_indices = dict()
a379775_indices[2] = 1
max_a379775_len=1000
while len(a379775) <= max_a379775_len:
    candidate = a379775[-1]
    done = False
    while not done:
        candidate = 2*candidate - 1
        factors = primefactors(candidate)
        for factor in factors:
            if factor not in a379775_indices:
                a379775.append(factor)
                a379775_indices[factor] = len(a379775)
                done = True
                break
a379776 = get_a379776(a379775_indices)
print(a379776)