Formerly Composite Numbers
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!üȯṗ→+fotpN


1-indexed.
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Explanation

!üȯṗ→+fotpN  Implicit input, a number n.
          N  The list of positive integers [1,2,3,4,..
      f      Keep those
         p   whose list of prime factors
       ot    has a nonempty tail: [4,6,8,9,10,12,..
 ü           De-duplicate wrt this equality predicate:
     +       sum
    →        plus 1
  ȯṗ         is a prime number.
             Result is [4,9,10,15,16,..
!            Get n'th element.