cp's OEIS Frontend

A104387 Larger of two successive primes the average of which is a repdigit.

%I A104387 #17 Jun 30 2022 10:27:00
%S A104387 5,7,11,101,113,4447,111111113,555555555559,10000000000000061,
%T A104387 111111111111111131,444444444444444469,555555555555555555619,
%U A104387 777777777777777777777787,333333333333333333333333333333373,444444444444444444444444444444444497
%N A104387 Larger of two successive primes the average of which is a repdigit.
%C A104387 Lesser primes A104388, repdigits A104389. What is the next term?
%C A104387 The next term is 444444444444444444444444444444444497.  The first term with more than 100 digits is a(22) which has 109 digits. - _Harvey P. Dale_, Jun 28 2011
%H A104387 Michael S. Branicky, <a href="/A104387/b104387.txt">Table of n, a(n) for n = 1..31</a>
%F A104387 a(n) = prime(A104386(n)+1).
%t A104387 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 *)
%o A104387 (Python)
%o A104387 from itertools import count, islice
%o A104387 from sympy import isprime, prevprime
%o A104387 def agen():
%o A104387     for d in count(1):
%o A104387         ru = int("1"*d)
%o A104387         for r in range(ru, 10*ru, ru):
%o A104387             if r > 2:
%o A104387                 p = prevprime(r)
%o A104387                 if isprime(r + (r-p)) and prevprime(r+(r-p)) == p:
%o A104387                     yield 2*r - p
%o A104387 print(list(islice(agen(), 15))) # _Michael S. Branicky_, Jun 30 2022
%Y A104387 Cf. A054268, A104386, A104388, A104389.
%K A104387 nonn,base
%O A104387 1,1
%A A104387 _Zak Seidov_, Mar 04 2005
%E A104387 More terms from _Giovanni Resta_, Apr 05 2006