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A104386 Numbers k such that the average of the k-th and (k+1)-th primes is a repdigit. 3

%I #20 Jul 02 2022 09:29:14

%S 2,3,4,25,29,603,6363181,21366409911,279238341033925

%N Numbers k such that the average of the k-th and (k+1)-th primes is a repdigit.

%F (prime(k) + prime(k+1))/2 = repdigit.

%o (Python)

%o from itertools import count, islice

%o from sympy import isprime, prevprime, primepi

%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 primepi(p)

%o print(list(islice(agen(), 7))) # _Michael S. Branicky_, Jun 30 2022

%Y Cf. A054268.

%Y Corresponding primes A104387, A104388, repdigits A104389.

%K nonn,base,hard,more

%O 1,1

%A _Zak Seidov_, Mar 04 2005

%E a(8) from _Giovanni Resta_, Apr 05 2006

%E a(9) from _Michael S. Branicky_, Jul 02 2022

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Last modified May 18 01:49 EDT 2024. Contains 372613 sequences. (Running on oeis4.)