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%I #19 Apr 30 2013 14:42:30
%S 0,1,0,2,1,4,5,2,7,3,3,11,4,13,14,16,6,6,20,7,22,8,25,9,29,10,31,32,
%T 11,34,38,13,41,14,15,15,47,49,50,52,18,18,19,58,59,20,21,67,68,23,70,
%U 24,24,25,77,79,27,27,83,28,85,88,92,31,94,95,33,101
%N a(1) and a(3) are 0. For all other n, a(n) is the smallest k such that 10*k is adjacent to a multiple of the n-th prime.
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Divisibility_rule">Divisibility rule</a>
%e a(6) = 4 because 13 (the sixth prime) divides 39, which is adjacent to 40.
%t a[n_] := Block[{p = Prime[n], k = 0}, Mod[10, p] > 0 && While[! MemberQ[{1, p-1}, Mod[10*k, p]], k++]; k]; Array[a,68] (* _Giovanni Resta_, Apr 30 2013 *)
%K nonn
%O 1,4
%A _J. Lowell_, Apr 23 2013
%E a(20)-a(68) from _Giovanni Resta_, Apr 30 2013