A376750 Indices n where a run of primes begins in A376198.

2, 9, 23, 52, 110, 231, 472, 965, 1958, 3962, 7980, 16029, 32181, 64597, 129574, 259798, 520835, 1043833, 2091473, 4190135, 8392863, 16809322, 33661860, 67402676, 134952624, 270177158, 540861852, 1082667610, 2167106199, 4337519113, 8681255531, 17374202846, 34770433922, 69582458821, 139243546013, 278635987083

Offset: 1

Author

N. J. A. Sloane, Oct 03 2024

Keywords

• nonn

Crossrefs

Cf. A376198-A376201, A376751-A376754.

Programs

Python

from itertools import count, islice
from sympy import isprime, nextprime
def A376750_4gen(): # generator of terms for A376750..4
    an, smc, smp = 2, 4, 3,
    wasprime = startp = startn = endp = endn = rl = 0
    for n in count(2):
        if not isprime(an):
            if wasprime: # a run has ended
                endn, endp = n-1, wasprime
                yield startn, startp, endn, endp, rl
            an = smp if an == 2*smp else smc
            wasprime = 0 # False
        else:
            if not wasprime: # a run has started
                startn, startp, rl = n, an, 1
            else: rl += 1
            wasprime = an
            an = smp if smp < smc else smc
        if an == smp: smp = nextprime(smp)
        else:
            smc += 1
            while isprime(smc): smc += 1
print([out[0] for out in list(islice(A376750_4gen(), 15))]) # Michael S. Branicky, Oct 03 2024

Extensions

a(14)-a(33) from Michael S. Branicky, Oct 04 2024

a(34)-a(36) from Michael S. Branicky, Oct 07 2024