tribonacchi

tri.py

def classic_round(x):
    return int(x) if int(x)-x>=0.5 else int(x)+1
def tribonacci(n):
    sqrt33=33**0.5
    a1=(19+3*sqrt33)**(1/3)
    a2=(19-3*sqrt33)**(1/3)
    b=(586+102*sqrt33)**(1/3)
    c=(1/3*(a1+a2+1))**n 
    d=b**2-2*b+4
    return classic_round(3*b*(c/d))
print(tribonacci(5))
print(ro(3.5))