65 concurrent uasyncio worker threads on 28KB free RAM ESP-01s module MicroPython

collatz_async.py

import uasyncio as asyncio

N = 65
loop  = asyncio.get_event_loop(runq_len = N+1)

def collatz(x):
    yield x
    while x!=1:
        x = 3*x+1 if x%2==1 else x//2
        yield x

async def worker(x):
    global N
    c = 0
    for k in collatz(x):
        c = c+1
        await asyncio.sleep(0)

    print(x, c-1)
    N = N-1

class Waiting():
    def __await__(self):
        global N
        while N>0:  yield from asyncio.sleep(1)            
    __iter__ = __await__  # issue 2678

async def killer():
    await Waiting()

trash = [ loop.create_task(worker(N-x))  for x in range(N) ]

loop.run_until_complete( killer() )