A379900 a(n) = position of prime(n) in A379899, or a(n) = -1 if prime(n) is not in A379899.

1, 2, 5, 3, 4, 6, 7, 12, 13, 8, 14, 9, 10, 15, 16, 11, 17, 31, 18, 19, 32, 20, 21, 33, 34, 35, 22, 23, 36, 37, 24, 25, 38, 26, 39, 27, 40, 28, 29, 41, 30, 42, 73, 43, 44, 74, 75, 76, 77, 45, 46, 78, 47, 79, 48, 80, 49, 81, 50, 51, 82, 52, 83, 84, 53, 54, 85

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_a379900(a379899_indices):
    a379900 = []
    count = 1
    while True:
        p = prime(count)
        if p not in a379899_indices:
            break
        a379900.append(a379899_indices[p])
        count += 1
    return a379900
a379899 = [2]
a379899_indices = dict()
a379899_indices[2] = 1
max_a379899_len=1000
while len(a379899) <= max_a379899_len:
    candidate = a379899[-1]
    done = False
    while not done:
        candidate = candidate + 4
        factors = primefactors(candidate)
        for factor in factors:
            if factor not in a379899_indices:
                a379899.append(factor)
                a379899_indices[factor] = len(a379899)
                done = True
                break
a379900 = get_a379900(a379899_indices)
print(a379900)

Crossrefs

Cf. A379899.

Sequence in context: A011310 A075250 A216248 * A060127 A065184 A065181

Adjacent sequences: A379897 A379898 A379899 * A379901 A379902 A379903

Keyword

nonn,easy

Author

Robert C. Lyons, Jan 05 2025

Status

approved