def triangles():
    b=[1]
    yield b
    b= [1,1]
    yield b
    while 1:
        c = [1 for j in range(len(b) + 1)]
        for i in range(1,len(c)+1):
            if i!=1 and i!=len(c):
                c[i-1]=b[i-1]+b[i-2]
        b=c
        yield b