type Fibonacci<T extends number, C extends unknown[] = [0, 0, 0], A1 extends unknown[] = [0], A2 extends unknown[] = [0]> =
  T extends 1 | 2 ? 1
  : C["length"] extends T
  ? [...A1, ...A2]["length"]
  : Fibonacci<T, [...C, 0], [...A1, ...A2], A1>

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Fibonacci<3>, 2>>,
  Expect<Equal<Fibonacci<8>, 21>>,
]