p(k): 1+5+9+...+(4k-3)=k(2k-1)
p(k+1): 1+5+9+...+(4k-3)+(4k+4-3)=k(2k+2-1)
1+5+9+...+(4k-3)+(4k+1)=k(2k+1)=2k²+k
⇒1+5+9+....+(4k-3)+(4k+1)=k(2k-1)+(4k+1)=2k²-k+4k+1=2k²+3k+1
ceva e gresit... normal trebuia sa obtin 2k²+k... uite-te ..nu e scris gresit ex??