Proof of a congruence for harmonic numbers conjectured by Z.-W. Sun
  For a positive integer $n$ let $H_n=\sum_{k=1}^{n}1/k$ be the $n$th harmonic number. In this note we prove that for any prime $p\ge 7$,   $$ \sum_{k=1}^{p-1}\frac{H_k^2}{k^2} \equiv4/5pB_{p-5}\pmod{p^2},   $$ which confirms the conjecture recently proposed by Z. W. Sun. Furthermore, we also prove two similar congruences modulo $p^2$. 
Romeo Mestrovic
math.NT