A376200 Indices where primes appear in A376198.

2, 3, 9, 10, 11, 23, 24, 25, 26, 52, 53, 54, 55, 56, 57, 58, 59, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 472, 473, 474, 475, 476, 477, 478, 479, 480, 481, 482, 483, 484, 485, 486, 487, 488

Offset: 1

Author

N. J. A. Sloane, Oct 03 2024

Keywords

• nonn

Comments

The primes appear in order, so a(n) is also the index of prime(n) in A376198.

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..100000

Crossrefs

Cf. A376198, A376199, A376201, A376750-A376754.

Programs

Python

from itertools import count, islice
from sympy import isprime, nextprime
def agen(): # generator of terms
    an, smc, smp = 2, 4, 3
    for n in count(2):
        if not isprime(an):
            an = smp if an == 2*smp else smc
        else:
            yield n
            an = smp if smp < smc else smc
        if an == smp: smp = nextprime(smp)
        else:
            smc += 1
            while isprime(smc): smc += 1
print(list(islice(agen(), 71))) # Michael S. Branicky, Oct 03 2024