a * a = 9*b +1
pt. b=1 ... a*a=9*1+1 =10 nu convine ;
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b=6 ... a*a=9*6+1=56 nu convine ;
b=7 ... a*a=9*7+1=64 = 8*8 deci a=8 ;
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b=11 ... a*a=9*11+1=100=10*10 deci a=10 ;
s.a.m.d.