7^(n-1):7^4= 7^(n+1-4)=7^(n-3) deci 7^(n-3)=49^2^3 dar 49=7^2,iar 2^3=8 echivalent cu (7^2)^8=7^16 deci revenind la primul rand de sus, aflam ca 7^(n-3)=7^16 deci n-3=16 => n=16+3