cmq... sarebbe :

2 + 4^-n < 2.00000001

4^-n < 0.00000001

ln 4^-n < ln 0.00000001 (= 1/100000000)

-n ln 4 < ln 1 - ln 100000000 (ln1=0)

-n < -ln 100000000/ln 4

10000000 = 10^8

-n < 8ln 10 / 2ln2

n > 4 ln 10 / ln 2----- > 4 ln2+ln5 /ln2 ...cioe 4ln2/ln2 + 4ln5/ln2

cioe 4 + 4ln5/ln2