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A083747 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. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,8

COMMENTS

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

LINKS

Table of n, a(n) for n=1..120.

Jon Perry, Wilde Primes.

EXAMPLE

a(8)=2 because 8 and 81 are composite but 811 is prime.

PROG

(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)); }

CROSSREFS

Cf. A069568.

Sequence in context: A113080 A174420 A011265 * A049334 A054924 A046751

Adjacent sequences:  A083744 A083745 A083746 * A083748 A083749 A083750

KEYWORD

base,sign

AUTHOR

Jason Earls (zevi_35711(AT)yahoo.com), Jun 16 2003

STATUS

approved

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Last modified July 23 22:29 EDT 2014. Contains 244873 sequences.