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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. Cf. A054268, A104386, A104387, A104388. Sequence in context: A317248 A115666 A245044 * A115655 A363248 A084350 Adjacent sequences: A104386 A104387 A104388 * A104390 A104391 A104392 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.)