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.

可以使用Python中的线程模块`threading`来实现多线程打印递增的数字。具体实现如下：

import threading

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

    def run(self):
        num = self.start_num
        while num <= self.end_num:
            self.lock.acquire()
            for i in range(self.step):
                print(num, end=' ')
                num += 1
            print()
            self.lock.release()

if __name__ == '__main__':
    lock = threading.Lock()
    t1 = PrintThread(1, 5, 5, lock)
    t2 = PrintThread(6, 10, 5, lock)
    t3 = PrintThread(11, 15, 5, lock)
    t4 = PrintThread(16, 20, 5, lock)
    t5 = PrintThread(21, 25, 5, lock)
    t6 = PrintThread(26, 30, 5, lock)
    t7 = PrintThread(31, 35, 5, lock)
    t8 = PrintThread(36, 40, 5, lock)
    t9 = PrintThread(41, 45, 5, lock)
    t10 = PrintThread(46, 50, 5, lock)
    t11 = PrintThread(51, 55, 5, lock)
    t12 = PrintThread(56, 60, 5, lock)
    t13 = PrintThread(61, 65, 5, lock)
    t14 = PrintThread(66, 70, 5, lock)
    t15 = PrintThread(71, 75, 5, lock)

    t1.start()
    t2.start()
    t3.start()
    t4.start()
    t5.start()
    t6.start()
    t7.start()
    t8.start()
    t9.start()
    t10.start()
    t11.start()
    t12.start()
    t13.start()
    t14.start()
    t15.start()

    t1.join()
    t2.join()
    t3.join()
    t4.join()
    t5.join()
    t6.join()
    t7.join()
    t8.join()
    t9.join()
    t10.join()
    t11.join()
    t12.join()
    t13.join()
    t14.join()
    t15.join()

该程序中创建了15个`PrintThread`线程对象，每个线程对象分别负责打印一段数字序列。`PrintThread`类继承自`threading.Thread`类，重写了`run()`方法，实现了打印数字的逻辑。使用`threading.Lock()`类创建了一个互斥锁，确保线程间的输出不会交叉。最后使用`start()`方法启动线程，使用`join()`方法等待线程结束。