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Sequence of the Day for August 22

A105999: Vos Post’s semiprimeth recurrence.

{ 1, 4, 10, 26, 77, 235, 779, ... }
Just as with Wilson’s primeth recurrence (see A007097), we start with 1 (even though it’s neither prime nor semiprime) and for the following terms use the recurrence
a (n) = spa (n  − 1)
(the semiprime equivalent of Wilson’s
a (n) = pa (n  − 1)
). I wonder if in this sequence 4 is the only square of a prime? (Quickest way to check several terms is to look for
μ (a (n)) = 0
, provided of course one has several terms).

The following is in the <noinclude> ... </noinclude> section.

For more details about today's Sequence of the Day, see {{Sequence of the Day for August 22}}.

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