A100437 Number of distinct products i*j*k*l for 1 <= i <= j <= k <= l <= n.

1, 5, 15, 25, 55, 75, 140, 175, 225, 275, 448, 504, 770, 882, 1022, 1134, 1626, 1782, 2460, 2670, 2970, 3270, 4345, 4565, 5135, 5585, 6100, 6505, 8338, 8679, 10927, 11525, 12393, 13261, 14345, 14787, 18187, 19344, 20618, 21346, 25823, 26698

Offset: 1

Author

N. J. A. Sloane, Nov 21 2004

Keywords

• nonn

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..200

Crossrefs

Cf. A027425, A027430, A100435, A100436, A100438.

Programs

Maple

f:=proc(n) local i,j,k,l,t1; t1:={}; for i from 1 to n do for j from i to n do for k from j to n do for l from k 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, n}, {k, j, n}, {l, k, n}] ]]]; Table[ f[n], {n, 45}] (* Robert G. Wilson v, Dec 14 2004 *)

PARI

pr(n)=my(v=List());for(i=1,n, for(j=i,n, listput(v, i*j))); Set(v)
a(n)=my(u=List(),v=pr(n)); for(i=1,#v,for(j=i,#v,listput(u,v[i]*v[j]))); #Set(u) \\ Charles R Greathouse IV, Mar 04 2014

Extensions

More terms from Robert G. Wilson v, Dec 14 2004