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 A086981 a(n) = smallest k where (10^k+1)=0 mod prime(n)^2, or 0 if no such k exists. 3
 0, 0, 0, 21, 11, 39, 136, 171, 253, 406, 0, 0, 0, 0, 1081, 0, 1711, 1830, 0, 0, 292, 0, 0, 1958, 4656, 202, 1751, 0, 5886, 6328, 2667, 8515, 548, 3197, 11026, 0, 6123, 0, 13861, 0, 15931, 16290, 0, 18528, 9653, 0, 3165, 24753, 0, 26106, 27028, 0, 3615, 6275 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS For a given a(n)>0, all the values of k such that (10^k+1)=0 mod prime(n)^2 are given by the sequence a(n)*A005408, i.e. odd multiples of a(n). For example, for n=5, prime(5)=11, a(n)=11, the set of values of k for which (10^k+1)=0 mod 11^2 is 11*A005408=11,33,55,77,99,... All the terms of the sequence a(n) are integer multiples of prime(n) for primes <1000 except for a(93)=243 where prime(93)=487. LINKS Charles R. Greathouse IV, Sep 10, 2008, Table of n, a(n) for n = 1..4000 EXAMPLE a(4)=21 since 21 is least value of k for which (10^k+1)=0 mod 7^2. CROSSREFS Cf. A000040, A086982. Sequence in context: A252629 A213217 A300505 * A114011 A300943 A270790 Adjacent sequences: A086978 A086979 A086980 * A086982 A086983 A086984 KEYWORD nonn AUTHOR Ray Chandler, Jul 27 2003 STATUS approved

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Last modified September 29 14:18 EDT 2023. Contains 365771 sequences. (Running on oeis4.)