Writing special symbols (Mathematics, Statistics) in HTML

x-bar = x̄ = x̄ or x̄ (hex)
x-hat = x̂ = x̂ or x̂ (hex)
x-arrow = x⃗ = x⃗
degree = ° = °
left ceiling = ⌈ = ⌈
right ceiling = ⌉ = ⌉
left floor = ⌊ = ⌊
right floor = ⌋ = ⌋
real-numbers set = ℝ = ℝ
greek uppercase a = A = Α
function = ƒ =ƒ
Sum = ∑ = ∑
Hadamard product = ⊙ = ⊙
dot = ⋅ = ⋅
not equal = ≠ = ≠