What notation should I use to denote the sum of multiples of k smaller than n

Question

I want the clearest, simplest way to denote, for example, the sum of every multiple of 3 smaller than 62 which i could denote like: $$ \sum_{i=0}^{20}3i =0+3+6+…+60 $$ which was the way I found to write it, but when using variables it requires me to introduce the floor function: $$\sum_{i=0}^{\left \lfloor \frac{n}{k} \right \rfloor}ki $$ So I wanted to know what would be a better way to write it without requiring the floor function