My brother just saw this on the Paris Metro and asked what it is; unfortunately, it has defeated me.
$$ {T_N} ^ {(2)} - {T_{N-1}} ^ {(1)} = {(LRC)}_{N - \frac{1}{2}}, $$
Does anyone know what it is? The $T_N$ look a bit like Chebyshev polynomials but what is $LRC$? Sounds like electrical engineering but are Chebyshev polynomial related to $LRC$ circuits?
