OFFSET
1,5
MAPLE
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;
MATHEMATICA
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 *)
PROG
(Python)
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
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 21 2004
EXTENSIONS
More terms from Robert G. Wilson v, Dec 14 2004
STATUS
approved