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
A104387
Larger of two successive primes the average of which is a repdigit.
Original entry on oeis.org
5, 7, 11, 101, 113, 4447, 111111113, 555555555559, 10000000000000061, 111111111111111131, 444444444444444469, 555555555555555555619, 777777777777777777777787, 333333333333333333333333333333373, 444444444444444444444444444444444497
Offset: 1
-
Union[Flatten[Table[NextPrime/@Select[FromDigits/@Table[PadLeft[{i},n,i], {n,45}], Mean[{NextPrime[#],NextPrime[#,-1]}]==#&], {i,9}]]] (* Harvey P. Dale, Jun 28 2011 *)
-
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 2*r - p
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.
Comments