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Square array T(n,k), n>=1, k>=1, read by antidiagonals in which column k lists the positive integers whose number of divisors is not k.
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%I #13 Aug 11 2012 22:03:57

%S 2,3,1,4,4,1,5,6,2,1,6,8,3,2,1,7,9,5,3,2,1,8,10,6,4,3,2,1,9,12,7,5,4,

%T 3,2,1,10,14,8,7,5,4,3,2,1,11,15,10,9,6,5,4,3,2,1,12,16,11,11,7,6,5,4,

%U 3,2,1,13,18,12,12,8,7,6,5,4,3,2,1,14,20

%N Square array T(n,k), n>=1, k>=1, read by antidiagonals in which column k lists the positive integers whose number of divisors is not k.

%C Column k lists the numbers j such that A000005(j) <> k.

%e Column 2 lists the nonprimes A018252 because they are the positive integers whose number of divisors is not 2.

%e Array begins:

%e 2, 1, 1, 1, 1, 1, 1, 1, 1, 1,

%e 3, 4, 2, 2, 2, 2, 2, 2, 2,

%e 4, 6, 3, 3, 3, 3, 3, 3,

%e 5, 8, 5, 4, 4, 4, 4,

%e 6, 9, 6, 5, 5, 5,

%e 7, 10, 7, 7, 6,

%e 8, 12, 8, 9,

%e 9, 14, 10,

%e 10, 15,

%e 11,

%Y Columns (1-4): A020725, A018252, A213367, A210994.

%K nonn,tabl

%O 1,1

%A _Omar E. Pol_, Aug 11 2012