# How does the equation for min heap array indexing work?

The article makes the following statement:

If a given node is located at index 'x' in the array, its left child exists at index = 2x, and its right child exists at index = 2x + 1. Each node's parent exists at index = x / 2 (rounded down).

It gives this example:

This min heap is represented in the array [100, 19, 36, 17, 3, 25, 1, 2, 7].

But this doesn't jive with the preceding statement about indexing. 36 can be found at index 2, and 2 * 2 is 4. But index 4 is 3-- the right child of the 19 node, not the left child of the 36 node.

What am I missing here?

Start indexing at $$1$$, then everything will be fine.
Want to start at $$0$$? That is no problem, but one has to adjust the formula's. Children of $$x$$ can be found at $$2x+1$$ and $$2x+2$$.