U(2^1) = 2
U(2^2) = 4
U(2^3) = 8
U(2^4) = 6
U(2^5) = 2
U(2^6) = 4
................
Ciclul este (2,4,6,8).
Avem niste conditii.
1) Daca puterea n e impara:
a) Daca (n+1):2 -> impar => U(2^n) = 2
b) Daca (n+1):2 -> par => U(2^n) = 8
2) Daca puterea n e para:
a) Daca n:2 -> impar => U(2^n) = 4
b) Daca n:2 -> par => U(2^n) = 6
Noi avem 2^1981
→ 1981 impar:
→ (1981+1):2 = 1982:2 = 991 → impar => U( 2^1981) = 2
