A236554 Number of involutions in the quaternion ring over Z/(2^n)Z with i^2=j^2=1.
8, 64, 288, 1056, 4128, 16416, 65568, 262176
Offset: 1
Programs
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Mathematica
invo11[n_] := Length@Reduce[a^2 - b^2 + c^2 + d^2 ==1 && 2 a b== 0 && 2 a c == 0 && 2 a d == 0, Modulus -> n];Table[invo11[2^n],{n,8}]
Formula
a(n) = A236553(2^n).