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Number of distinct products i*j over all pairs (i,j) with i,j >= 0 and i+j <= n and gcd(i,j) <= 1.
2

%I #12 Aug 02 2019 20:58:27

%S 1,1,2,3,4,6,7,9,11,14,16,20,22,26,29,32,35,41,44,50,54,59,63,70,74,

%T 80,85,92,98,108,112,121,129,137,144,153,158,170,177,186,192,204,210,

%U 222,231,240,249,262,270,284,293,305,315,331,340,353

%N Number of distinct products i*j over all pairs (i,j) with i,j >= 0 and i+j <= n and gcd(i,j) <= 1.

%C Note that gcd(0,m) = m for any m.

%H Robert Price, <a href="/A225529/b225529.txt">Table of n, a(n) for n = 0..400</a>

%t f[n_]:=Length[Complement[Union[Flatten[Table[If[i+j≤n&&GCD[i,j]<=1, {i*j}], {i, 0, n}, {j, 0, n}], 1]], {Null}]]; Table[f[n], {n, 0, 100}]

%Y Cf. A018805, A027430, A100448, A100449, A100450, A213207, A213208.

%K nonn,easy

%O 0,3

%A _Robert Price_, May 09 2013