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A083747
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Smallest number m such that n followed by m ones yields a prime; a(p) = 0 because 0 ones are necessary to yield a prime.
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3
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1, 0, 0, 1, 0, 1, 0, 2, 2, 1, 0, 136, 0, 9, 1, 3, 0, 1, 0, 2, 1, 3, 0, 1, 1, 3, 1, 1, 0, 2, 0, 35, 1, 6, 2, 4, 0, -1, 2, 1, 0, 1, 0, 3, 772, 1, 0, 5, 1, 2, 4, 1, 0, 1, 31, 18470, 1, 3, 0, 1, 0, 2, 1, 1, 3, 1, 0, 3, 1, 1, 0, 2, 0, 2, 1, 1, 9, 4, 0, 2, 1, 1, 0, 5, 6, 3, 149, 1, 0, 2, 1, 3, 2, 1, 2, 7, 0, 2, 1, 10, 0, 1, 0, 44, 1, 1, 0, 5, 0, 17, 16, 3, 0, 2, 1, 9, 1, 1, 5, 1
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OFFSET
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1,8
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COMMENTS
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a(38) = -1 means no prime has yet been found; a(176) = -1 because it has been proved never to reach a prime. a(45) = 772 and a(56) = 18470 found by Richard Heylen; a(45) has been proved prime while a(56) is 3-PRP.
Number of times 1 has to be repeatedly appended to n to form a prime. - Lekraj Beedassy, Jun 01 2006
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LINKS
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Table of n, a(n) for n=1..120.
Jon Perry, Wilde Primes.
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EXAMPLE
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a(8)=2 because 8 and 81 are composite but 811 is prime.
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PROG
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(PARI) { aop(n) = local(c, k, stop); c=0; k=n; stop=500; if(isprime(n), return(0)); while(!isprime(k) && c<stop, k=k*10+1; c++); if(c<stop, return(c), return(-1)); }
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CROSSREFS
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Cf. A069568.
Sequence in context: A113080 A174420 A011265 * A049334 A054924 A046751
Adjacent sequences: A083744 A083745 A083746 * A083748 A083749 A083750
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KEYWORD
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base,sign
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AUTHOR
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Jason Earls (zevi_35711(AT)yahoo.com), Jun 16 2003
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STATUS
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approved
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