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A114429
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Larger of the greatest twin prime pair with n digits.
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4
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7, 73, 883, 9931, 99991, 999961, 9999973, 99999589, 999999193, 9999999703, 99999999763, 999999999961, 9999999998491, 99999999999973, 999999999997969, 9999999999999643, 99999999999998809, 999999999999998929
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OFFSET
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1,1
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COMMENTS
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Also the denominator of the largest prime over prime fraction less than 10^n.
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LINKS
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FORMULA
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PROG
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(Python)
import sympy
for i in range(1, 100):
p=sympy.prevprime(10**i)
while not sympy.isprime(p-2):
p=sympy.prevprime(p)
print(p)
(PARI)
a(n)=my(p=precprime(10^n)); while(!ispseudoprime(p-2), p=precprime(p-1)); return(p)
vector(50, n, a(n)) \\ Derek Orr, Aug 02 2014
(PARI) apply( {A114429(n, p=10^n)=until(2==p-p=precprime(p-1), ); p+2}, [1..22]) \\ twice as fast by avoiding additional ispseudoprime(). - M. F. Hasler, Jan 17 2022
(Python)
from sympy import prevprime
def a(n):
p = prevprime(10**n); pp = prevprime(p)
while p - pp != 2: p, pp = pp, prevprime(pp)
return p
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CROSSREFS
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Cf. A092250 (a(n)-2: lesser of the pair).
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KEYWORD
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base,easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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