Mbpp/739

import math
def find_Index(n: int) -> int:
    """
    Returns the index k of the smallest triangular number T_k = k*(k+1)//2
    that has exactly n digits (or at least n digits? Actually "with n digits" implies the smallest triangular number whose number of digits is n).
    The smallest k such that T_k >= 10^(n-1).
    """
    if n <= 0:
        raise ValueError("n must be a positive integer")
    target = 2 * 10**(n - 1)
    k = math.isqrt(target)
    # Adjust k if k*(k+1) is smaller than target
    if k * (k + 1) < target:
        k += 1
    return k

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