Find the sum of all numbers below n that are a multiple of some set of numbers
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ḍþṖḅTS


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How it works

ḍþṖḅTS  Main link. Left argument: D (array). Right argument: n (integer)

ḍþ       Divisible table; test each k in [1, ..., n] for divisibility by all
        integers d in D.
  Ṗ     Pop; discard the last Boolean array, which corresponds to n.
   ḅ    Unbase; convert the Boolean arrays of base n to integer. This yields a 
        non-zero value (truthy) and and only if the corresponding integer k is 
        divisible by at least one d in D.
    T   Truth; yield the array of all indices of truthy elements.
     S  Compute their sum.