The differences are: 6-8=-2, 9-6=3, 23-9=14, 87-23=64. These are -2, 3, 14, 64. Their differences are: 5, 11, 50. Alternatively: 0-2=-2, 3+0=3, 3×4+2=14, 14×4+8=64. The next would be 64×4+16=272, so 87+272=359. But if pattern is powers of 4 minus multiples, could be 429.