I have a Bachelor's degree in physics and I enjoy advanced calculus but my real interest goes to logarithmic/ polylogarithmic integrals and harmonic series.

I wrote a book about the harmonic series (An Introduction To The Harmonic Series And Logarithmic Integrals) and it's available on Amazon https://www.amazon.com/Introduction-Harmonic-Logarithmic-Integrals-Researchers/dp/1736736000

The eBook PDF can be found for free on https://www.researchgate.net/publication/373488370_An_Introduction_To_the_Harmonic_Series_And_Logarithmic_Integrals-For_High_School_Students_Up_To_Researchers