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%I #9 Oct 16 2023 23:30:24
%S 0,0,0,1,5,13,29,50,79,111,186,219,345,428,513,610,884,991,1387,1535,
%T 1742,1994,2671,2833,3319,3719,4154,4474,5751,5985,7575,8121,8803,
%U 9593,10401,10785,13303,14371,15414,15988,19379,20089,24103,25237,26369
%N Number of distinct products i*j*k*l for 1 <= i < j < k < l <= n.
%p f:=proc(n) local i,j,k,l,t1; t1:={}; for i from 1 to n-3 do for j from i+1 to n-2 do for k from j+1 to n-1 do for l from k+1 to n do t1:={op(t1),i*j*k*l}; od: od: od: od: t1:=convert(t1,list); nops(t1); end;
%t f[n_] := Length[ Union[ Flatten[ Table[ i*j*k*l, {i, n}, {j, i + 1, n}, {k, j + 1, n}, {l, k + 1, n}]]]]; Table[ f[n], {n, 45}] (* _Robert G. Wilson v_, Dec 14 2004 *)
%o (Python)
%o def A100438(n): return len({i*j*k*l for i in range(1,n+1) for j in range(1,i) for k in range(1,j) for l in range(1,k)}) # _Chai Wah Wu_, Oct 16 2023
%Y Cf. A027425, A027430, A100435, A100436, A100437.
%K nonn
%O 1,5
%A _N. J. A. Sloane_, Nov 21 2004
%E More terms from _Robert G. Wilson v_, Dec 14 2004
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