Status: IN
`is_prime` uses a hardcoded set `{2,3,5,7,11,13,17,19}` that is correct for all integers 0–20, sufficient for inputs up to `2^20 - 1` (the problem's upper bound); extending beyond 20-bit inputs would require adding primes up to the new bit width
Source: entries/2026/06/06/prime-number-of-set-bits-in-binary-representation-solution.md