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A069531 Smallest positive k such that 10^k + 1 is divisible by n, or 0 if no such number exists. 2
1, 0, 0, 0, 0, 0, 3, 0, 0, 0, 1, 0, 3, 0, 0, 0, 8, 0, 9, 0, 0, 0, 11, 0, 0, 0, 0, 0, 14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 23, 0, 21, 0, 0, 0, 0, 0, 0, 0, 0, 0, 29, 0, 30, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 22, 0, 3, 0, 0, 0, 0, 0, 48, 0, 0, 0, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,7

COMMENTS

When a(n) is not zero, it is a divisor of phi(n). If n is a prime with primitive root 10 (cf. A001913) then a(n) = (n-1)/2.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10001

EXAMPLE

a(7) = a(13) = 3 as 1001 is divisible by 7 and 13. a(17) = 8 as 17 divides 100000001 = 10^8 + 1.

PROG

(PARI) A069531(n) = { fordiv(eulerphi(n), k, if(!((1+(10^k))%n), return(k))); (0); }; \\ Antti Karttunen, Aug 23 2019

CROSSREFS

Cf. A069521 to A069530.

Cf. A000010, A001913, A002329.

Sequence in context: A096693 A193139 A083206 * A035677 A143276 A283470

Adjacent sequences:  A069528 A069529 A069530 * A069532 A069533 A069534

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Apr 01 2002

EXTENSIONS

More terms from Vladeta Jovovic, Apr 03 2002

STATUS

approved

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Last modified September 18 12:29 EDT 2019. Contains 327170 sequences. (Running on oeis4.)