login
A376750
Indices n where a run of primes begins in A376198.
10
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
1,1
PROG
(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
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, 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
STATUS
approved