Are you sure about the first rule? It doesn't seem necessary according to https://oeis.org/A014575.
The problem is really fun.
Since I created the problem series and want the Functions I badge, I thought I'd provide the solution that incorporates vampire_factor and are_fangs. Not a great score, but readable!
Sorry, I mean the Magic Numbers badge.
Which values occur exactly three times?
Alphabetize by last name
Back to basics 5 - Clipboard
Find perfect placement of non-rotating dominoes (easier)
Rotate a Matrix by 90 degrees
Multivariate polynomials - emulate symbolic form
Multivariate polynomials - overload multiplication
Find all vampire fangs
Negation the hard way
Product of two multivariate polynomials
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