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A104388 Lesser of two successive primes the average of which is a repdigit. 5
3, 5, 7, 97, 109, 4441, 111111109, 555555555551, 9999999999999937, 111111111111111091, 444444444444444419, 555555555555555555491, 777777777777777777777767, 333333333333333333333333333333293, 444444444444444444444444444444444391 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..31

FORMULA

a(n) = prime(A104386(n)).

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 p

print(list(islice(agen(), 15))) # Michael S. Branicky, Jun 30 2022

CROSSREFS

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

KEYWORD

nonn,base

AUTHOR

Zak Seidov, Mar 04 2005

EXTENSIONS

More terms from Giovanni Resta, Feb 09 2006

STATUS

approved

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Last modified February 6 01:28 EST 2023. Contains 360091 sequences. (Running on oeis4.)