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// SumSquare returns the total number of grains to n-th square.
// SumSquare(64) == Total()
func SumSquare(n int) (uint64, error) {
if n < 1 || n > 64 {
return 0, fmt.Errorf("input must be positive and <= 64, got: %q", n)
}
return 1<<n - 1, nil
}