A104388
Lesser of two successive primes the average of which is a repdigit.
Original entry on oeis.org
3, 5, 7, 97, 109, 4441, 111111109, 555555555551, 9999999999999937, 111111111111111091, 444444444444444419, 555555555555555555491, 777777777777777777777767, 333333333333333333333333333333293, 444444444444444444444444444444444391
Offset: 1
-
from itertools import count, islice
from sympy import isprime, prevprime
def agen():
for d in count(1):
ru = int("1"*d)
for r in range(ru, 10*ru, ru):
if r > 2:
p = prevprime(r)
if isprime(r + (r-p)) and prevprime(r+(r-p)) == p:
yield p
print(list(islice(agen(), 15))) # Michael S. Branicky, Jun 30 2022
A104389
Repdigits which are the average of two successive primes.
Original entry on oeis.org
4, 6, 9, 99, 111, 4444, 111111111, 555555555555, 9999999999999999, 111111111111111111, 444444444444444444, 555555555555555555555, 777777777777777777777777, 333333333333333333333333333333333, 444444444444444444444444444444444444
Offset: 1
-
from itertools import count, islice
from sympy import isprime, prevprime
def agen():
for d in count(1):
ru = int("1"*d)
for r in range(ru, 10*ru, ru):
if r > 2:
p = prevprime(r)
if isprime(r + (r-p)) and prevprime(r+(r-p)) == p:
yield r
print(list(islice(agen(), 15))) # Michael S. Branicky, Jun 30 2022
A104386
Numbers k such that the average of the k-th and (k+1)-th primes is a repdigit.
Original entry on oeis.org
2, 3, 4, 25, 29, 603, 6363181, 21366409911, 279238341033925, 2907021742443974, 11220808305309952, 11885037375341198280
Offset: 1
-
from itertools import count, islice
from sympy import isprime, prevprime, primepi
def agen():
for d in count(1):
ru = int("1"*d)
for r in range(ru, 10*ru, ru):
if r > 2:
p = prevprime(r)
if isprime(r + (r-p)) and prevprime(r+(r-p)) == p:
yield primepi(p)
print(list(islice(agen(), 7))) # Michael S. Branicky, Jun 30 2022
Showing 1-3 of 3 results.