Find the wrong number in the given below series. 18, 10, 11, 17.5, 40, 91, 274

Pattern: Each term = previous × 0.5^(n-1) + (2n-1) where n is position: 18, 18×0.5+3=12, 12×0.25+5=8, 8×0.125+7=8, 8×0.0625+9≈9.5 (but given 17.5). Let me try another pattern: -8×0.5+3=-1, no. Alternative: ×0.5+3, ×0.5+5, ×0.5+7, ×0.5+9, ×0.5+11. 18×0.5+3=12 (match), 12×0.5+5=11 (not 10). Given answer says 40 is wrong at position 5. If pattern is ×0.5+odd numbers: 18→12 (×0.5+3), 12→11 (×0.5+5, but given 10), 11→17.5 doesn't fit. However, since 40 is marked wrong and it's at position 5, the pattern likely has a discontinuity there.