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Array read by antidiagonals: T(m,n) is the number of distinct products ij with 1<=i<=m, i<=j<=n, for m>=1, n>=1.
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%I #4 Mar 30 2012 17:37:18

%S 1,2,2,3,3,3,4,5,5,4,5,6,6,6,5,6,8,8,8,8,6,7,9,11,9,11,9,7,8,11,12,13,

%T 13,12,11,8,9,12,15,15,14,15,15,12,9,10,14,17,19,17,17,19,17,14,10,11,

%U 15,18,20,22,18,22,20,18,15,11,12,17,20,22,24,24,24,24,22,20,17,12,13,18,23,24,27,27,25,27,27,24,23,18,13

%N Array read by antidiagonals: T(m,n) is the number of distinct products ij with 1<=i<=m, i<=j<=n, for m>=1, n>=1.

%e Array begins:

%e 1 2 3 4 5 6 7 8 9 10 ...

%e 2 3 5 6 8 9 11 12 14 15 ...

%e 3 5 6 8 11 12 15 17 18 20 ...

%e 4 6 8 9 13 15 19 20 22 24 ...

%e 5 8 11 13 14 17 22 24 27 28 ...

%p T := (m,n) -> nops({seq(seq(i*j, i=1..m),j=1..n)});

%t T[m_, n_] := Length[Union @@ Table[i*j, {i, m}, {j, n}]]

%Y A027424 is the main diagonal.

%K nonn,tabl

%O 1,2

%A _Michael Kleber_, Jul 09 2003