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A373859
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Smallest prime obtained by appending one or more 9's to n, -1 if no such prime exists.
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1
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19, 29, -1, 499, 59, -1, 79, 89, -1, 109, 1199999, -1, 139, 149, -1, 1699, 179, -1, 199, 2099, -1, 229, 239, -1, 25999, 269, -1, 289999, 2999, -1, 319999999999999999999999999999, 3299, -1, 349, 359, -1, 379, 389, -1, 409, 419, -1, 439, 449, -1
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OFFSET
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1,1
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LINKS
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FORMULA
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a(11) = 1199999 because 119, 1199, 11999 and 119999 are not primes.
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PROG
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(Python)
from itertools import count
from sympy import isprime
def A373859(n): return next(p for p in ((n+1)*10**m-1 for m in count(1)) if isprime(p)) if n%3 else -1 # Chai Wah Wu, Jul 08 2024
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CROSSREFS
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KEYWORD
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base,sign
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AUTHOR
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STATUS
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approved
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