3D Visual Block Sequence

A block sequence in three dimensions. We can write a formula for this one:

Create a function that takes a number (step) as an argument and returns the amount of blocks in that step.

Examples

blocks(1) ➞ 5

blocks(5) ➞ 39

blocks(2) ➞ 12

Notes

• Step 0 obviously has to return 0.
• The input is always a positive integer.