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A104388
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Lesser of two successive primes the average of which is a repdigit.
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5
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3, 5, 7, 97, 109, 4441, 111111109, 555555555551, 9999999999999937, 111111111111111091, 444444444444444419, 555555555555555555491, 777777777777777777777767, 333333333333333333333333333333293, 444444444444444444444444444444444391
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listen;
history;
text;
internal format)
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OFFSET
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1,1
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LINKS
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Chai Wah Wu, Table of n, a(n) for n = 1..31
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FORMULA
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a(n) = prime(A104386(n)).
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PROG
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(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 p
print(list(islice(agen(), 15))) # Michael S. Branicky, Jun 30 2022
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CROSSREFS
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Cf. A054268, A104386, A104387 (larger primes), A104389 (repdigits).
Sequence in context: A082697 A051345 A242387 * A110337 A132287 A046201
Adjacent sequences: A104385 A104386 A104387 * A104389 A104390 A104391
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KEYWORD
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nonn,base
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AUTHOR
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Zak Seidov, Mar 04 2005
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EXTENSIONS
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More terms from Giovanni Resta, Feb 09 2006
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STATUS
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approved
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