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A235203
Positive integers not represented by xyzw + xy + yz + zw + wx when evaluated over the positive integers.
0
1, 2, 3, 4, 6, 7, 9, 10, 15, 19, 22, 30, 37, 42, 57, 70, 79, 187, 190, 274, 715, 1317
OFFSET
1,2
COMMENTS
No other terms < 10^8. Sequence is probably finite. - Giovanni Resta, Jan 04 2014
MAPLE
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);
#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
CROSSREFS
Sequence in context: A076679 A339509 A060233 * A187102 A191991 A369138
KEYWORD
nonn
AUTHOR
C. Carroll, Jan 04 2014
STATUS
approved