启动3个线程打印递增的数字, 线程1先打印1,2,3,4,5, 然后是线程2打印6,7,8,9,10, 然后是线程3打印11,12,13,14,15. 接着再由线程1打印16,17,18,19,20….以此类推, 直到打印到75.

好的，我可以为您提供一个Python的示例代码，如下所示：

import threading

class PrintThread(threading.Thread):
    def __init__(self, start_num, end_num, step, lock):
        super().__init__()
        self.start_num = start_num
        self.end_num = end_num
        self.step = step
        self.lock = lock

    def run(self):
        for i in range(self.start_num, self.end_num+1, self.step):
            with self.lock:
                print(i, end=" ")
        print()

if __name__ == "__main__":
    lock = threading.Lock()
    thread1 = PrintThread(1, 5, 1, lock)
    thread2 = PrintThread(6, 10, 1, lock)
    thread3 = PrintThread(11, 15, 1, lock)

    thread1.start()
    thread2.start()
    thread3.start()

    thread1.join()
    thread2.join()
    thread3.join()

    for i in range(16, 76, 15):
        with lock:
            for j in range(i, i+5):
                print(j, end=" ")
            print()

这里我们定义了一个PrintThread类，每个线程通过传入的参数来打印指定的数字范围。同时，我们使用了一个Lock来保证线程安全，避免多个线程同时打印同一个数字。接下来我们启动三个线程来打印1-15的数字，然后再通过循环打印16-75的数字。