Abstract
In this study we find bases of S ₆(Γ ₀(23)), S ₈(Γ ₀(23)) and obtain explicit formulae for the number of representations of numbers by some quadratic forms in 12 and 16 variables that are direct sums of binary quadratic forms F₁ = x₁² + x₁ x₂ + 6x₂² and Φ₁ = 2x₁² + x₁x₂ + 3x₂² (or its inverse) with discriminant −23.