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A243294
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Least number k > 1 such that a number composed of k consecutive ascending digits starting with n is prime.
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0
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OFFSET
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1,1
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COMMENTS
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After the digit 9 comes 0 and it repeats.
If k could equal 1, the sequence becomes {171, 1, 1, 4, 1, 2, 1, 2, 13}.
It is interesting that when n is prime, a(n) is prime.
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LINKS
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EXAMPLE
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78 is not prime. 789 is not prime. 7890 is not prime. 78901 is prime. Thus a(7) = 5 since 78901 is a 5-digit number.
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PROG
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(Python)
import sympy
from sympy import isprime
def a(n):
....num = str(n)
....for i in range(n+1, 10**3):
........num += str(i%10)
........if isprime(int(num)):
............return len(num)
n=1
while n < 10:
....print(a(n), end=', ')
....n+=1
(PARI) a(n) = {s = Str(n); i = n+1; while (1, if (i==10, i = 0); s = concat(s, i); i++; if (isprime(eval(s)), return (length(s))); ); } \\ Michel Marcus, Jun 04 2014
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CROSSREFS
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KEYWORD
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nonn,base,full,fini
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AUTHOR
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STATUS
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approved
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