A104389 - OEIS

%I #8 Jun 30 2022 10:25:18

%S 4,6,9,99,111,4444,111111111,555555555555,9999999999999999,

%T 111111111111111111,444444444444444444,555555555555555555555,

%U 777777777777777777777777,333333333333333333333333333333333,444444444444444444444444444444444444

%N Repdigits which are the average of two successive primes.

%H Michael S. Branicky, <a href="/A104389/b104389.txt">Table of n, a(n) for n = 1..31</a>

%F a(n) = (A104387(n)+A104388(n))/2.

%o (Python)

%o from itertools import count, islice

%o from sympy import isprime, prevprime

%o def agen():

%o     for d in count(1):

%o         ru = int("1"*d)

%o         for r in range(ru, 10*ru, ru):

%o             if r > 2:

%o                 p = prevprime(r)

%o                 if isprime(r + (r-p)) and prevprime(r+(r-p)) == p:

%o                     yield r

%o print(list(islice(agen(), 15))) # _Michael S. Branicky_, Jun 30 2022

%Y Corresponding primes: A104387, A104388.

%Y Cf. A054268, A104386, A104387, A104388.

%K nonn,base

%O 1,1

%A _Zak Seidov_, Mar 04 2005

%E More terms from _Giovanni Resta_, Apr 05 2006