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Origin of EIS sequences A045895 & A045896


When laying in bed I stared at the ceiling of my dorm room. It was subdivided by four beams into three fields. Label them 1 2 3. Involuntarily I started counting 1-2-3-1-2-3, the eyes going like a pendulum from left to right to left etc. Now I had the pairs:
  Counting:       1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3
  Label of field: 1 2 3 2 1 2 3 2 1 2 3 2 1 2 3 2 1 2 3 2 1 2 3 2
I started wondering about these pairs of numbers. Obviously they are periodic. In general, the period of "Counting" is n, the period of "Label of field" is 2n-2, where n is the number of fields. The period of the pairs is LCM(2n-2,n). That lead me to:
Mathematica> Table[LCM[2*n-2,n], {n, 16}]

{0, 2, 12, 12, 40, 30, 84, 56, 144, 90, 220, 132, 312, 182, 420, 240}
This is EIS sequence A045895.

Of course, all elements of this sequence are a multiple of 2. Dividing by 2 yields:

Mathematica> Table[LCM[2*n-2,n]/2, {n, 16}]

{0, 1, 6, 6, 20, 15, 42, 28, 72, 45, 110, 66, 156, 91, 210, 120}
This is EIS sequence A045896.
Ralf W. Grosse-Kunstleve <rwgk@cci.lbl.gov>