EN
Let $λ_f(n)$ be the nth normalized Fourier coefficient of a holomorphic or Maass cusp form f for SL(2,ℤ). We establish the asymptotic formula for the summatory function
$∑_{\substack{n≤x\\ n≡l (mod q)}} |λ_f(n)|^{2j}$
as x → ∞, where q grows with x in a definite way and j = 2,3,4.