Hiring process8 levels
  1. 1 IQ Test
  2. 2 Additional Online Test (If Required)
  3. 3 Office Interview with Hiring Manager
  4. 4 Unpaid Test Task (Motivation Check)
  5. 5 Paid Test Task and Follow-Up Interview
  6. 6 Iterative Paid Test Tasks
  7. 7 Office Verification
  8. 8 Final Interview with the Founder

Problems > Pentagonal Numbers > Editorial

Pentagonal Numbers — Solution & Editorial

Back to the Problem

Apply the closed form directly — derive it by pairing/telescoping if unfamiliar.

Complexity: O(1)

Watch out: The result overflows 32-bit — use 64-bit (or big) integers.