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 A104386 Numbers k such that the average of the k-th and (k+1)-th primes is a repdigit. 3
 2, 3, 4, 25, 29, 603, 6363181, 21366409911, 279238341033925 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..9. FORMULA (prime(k) + prime(k+1))/2 = repdigit. PROG (Python) from itertools import count, islice from sympy import isprime, prevprime, primepi 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 primepi(p) print(list(islice(agen(), 7))) # Michael S. Branicky, Jun 30 2022 CROSSREFS Cf. A054268. Corresponding primes A104387, A104388, repdigits A104389. Sequence in context: A055006 A139050 A043309 * A171558 A044906 A255312 Adjacent sequences: A104383 A104384 A104385 * A104387 A104388 A104389 KEYWORD nonn,base,hard,more AUTHOR Zak Seidov, Mar 04 2005 EXTENSIONS a(8) from Giovanni Resta, Apr 05 2006 a(9) from Michael S. Branicky, Jul 02 2022 STATUS approved

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Last modified April 13 11:28 EDT 2024. Contains 371640 sequences. (Running on oeis4.)