And of course I forgot that ** is the bold markup over here.
Fixes:
C(n) = 41 * 4^n + 5 * 4^(n-1) + 5 * 4^(n-2) + ... + 5 * 4 + 5
C(n) = 36 * Q + 5 * Q * (1 + 1/4 + 1/4^2 + ... + 1/4^n)
The latter two terms in the denominator, a constant and a term proportional to 2^n, become insignificant compared to the dominant term proportional to 2^(2*n) as n grows, so in the limit they do not influence the ratio and can be ignored.