If a sequence contains only whole numbers, which of these sequences could include the term 27, if a1 does not equal 27?

Each recurrence can include 27 if some whole-number starting value other than 27 produces it in a later term. For B, starting with 13 gives 27 next; for C, starting with 9 gives 27; and for D, starting with 21 gives 27. A only doubles, so it cannot reach the odd number 27 from a whole-number starting value. For E, the terms follow the pattern 3a + 1, and solving for a term to be 27 would require a whole-number starting value that is not possible.

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