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

1,2

Links

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

Prog

(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)

Crossrefs

Cf. A379775.

Sequence in context: A097723 A187831 A087786 * A210468 A080950 A023852

Adjacent sequences: A379773 A379774 A379775 * A379777 A379778 A379779

Keyword

nonn,easy

Author

Robert C. Lyons, Jan 02 2025

Status

approved