i=2 => s=2+416+18+20+6+8+10+12+14+16+18+20
i=4=> s=s+4+6+18+20+6+8+10+12+14+16+18+20
i=6=> s=s+6+18+20+6+8+10+12+14+16+18+20
i=8=> s=s+8+20+6+8+10+12+14+16+18+20
......................................................................
i=18=> s=s+18+20
i=20=> s=s+20
Deci:
s=2*1+4*2+6*3+8*4+10*5+12*6+14*7+16*8+18*9+20*10
Pentru punctul b trebuie vazut pentru ce valoare n obtinem acea valoare:
2*1+4*2+6*3+8*4+10*5+12*6+14*7+16*8+18*9+20*10 + ,,,+ n*n/2=656700