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%I #9 Jan 11 2014 12:37:04
%S 1,2,3,4,6,7,9,10,15,19,22,30,37,42,57,70,79,187,190,274,715,1317
%N Positive integers not represented by xyzw + xy + yz + zw + wx when evaluated over the positive integers.
%C No other terms < 10^8. Sequence is probably finite. - _Giovanni Resta_, Jan 04 2014
%p f := proc (x, y, z, w) x*y*z*w+x*y+y*z+z*w+w*x end proc: N := 1500: S := {}: for i to floor(N^(1/4)) do for j to floor((N/i)^(1/3)) do for k to floor((N/(i*j))^(1/2)) do for l to floor(N/(i*j*k)) do S := {f(i, j, k, l), f(i, j, l, k), f(i, k, j, l), op(S)} end do end do end do end do: `minus`({seq(i, i = 1 .. N)}, S);
%p #Note: f is invariant under a dihedral permutation of (x,y,z,w); the above program finds elements of the sequence with choice of upper bound N = 1500
%K nonn
%O 1,2
%A _C. Carroll_, Jan 04 2014