4, 6, 12, 30, 75, 315, 1260

Solution

The pattern of the number series is as given below

6 = 4*1.5

12 = 6*2
30 = 12*2.5
90 = 30*3
315 = 90*3.5
1260 = 315*4

Hence, the number which is wrong in the given series is 75 (it should have been 90)

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