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A104389 Repdigits which are the average of two successive primes. 4
4, 6, 9, 99, 111, 4444, 111111111, 555555555555, 9999999999999999, 111111111111111111, 444444444444444444, 555555555555555555555, 777777777777777777777777, 333333333333333333333333333333333, 444444444444444444444444444444444444 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..31
FORMULA
a(n) = (A104387(n)+A104388(n))/2.
PROG
(Python)
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
CROSSREFS
Corresponding primes: A104387, A104388.
Sequence in context: A317248 A115666 A245044 * A115655 A363248 A084350
KEYWORD
nonn,base
AUTHOR
Zak Seidov, Mar 04 2005
EXTENSIONS
More terms from Giovanni Resta, Apr 05 2006
STATUS
approved

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Last modified May 18 02:04 EDT 2024. Contains 372615 sequences. (Running on oeis4.)