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A241147 a(n) = the number of integers i in {1,2,...,L}, where L = lcm(1,2,...,n), having the property that the number of positive integer divisors of i that are less than or equal to n, is odd. 0

%I

%S 1,1,3,7,33,33,225,405,1305,1235,13635,13635,177705,170775,170181,

%T 359073,6106815,5919705,112887225,109706355,110362725,107787735

%N a(n) = the number of integers i in {1,2,...,L}, where L = lcm(1,2,...,n), having the property that the number of positive integer divisors of i that are less than or equal to n, is odd.

%e For n = 4 we have a(n) = 7, since the divisors <=4 of 1,2,..., 12 are

%e {1}, {1,2}, {1,3}, {1,2,4}, {1}, {1,2,3}, {1}, {1,2,4}, {1,3}, {1,2}, {1}, and {1,2,3,4}, and only 7 of these have odd cardinality.

%K nonn

%O 1,3

%A _Jeffrey Shallit_, Apr 16 2014

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Last modified September 20 16:46 EDT 2019. Contains 327242 sequences. (Running on oeis4.)