Leysa a_{n}=4*(-5)^n-1,quadn

$$a _ { n } = 4 \cdot ( - 5 ) ^ { n - 1 } , \quad n$$

Leystu fyrir a_n (complex solution)

$$a_{n}=-\frac{4\left(-5\right)^{n}}{5}$$

Leystu fyrir n (complex solution)

$$n=\frac{\ln(a_{n})-\ln(\frac{4}{5})+\pi i}{\ln(5)+\pi i}+\frac{2\pi n_{1}i}{\ln(5)+\pi i}$$

$$n_{1}\in \mathrm{Z}$$

$$a_{n}\neq 0$$

Leystu fyrir a_n

$$a_{n}=-\frac{4\left(-5\right)^{n}}{5}$$

$$Denominator(n)\text{bmod}2=1$$

Leystu fyrir n

$$n=\frac{\ln(a_{n})+\ln(\frac{5}{4})}{\ln(5)}$$

$$a_{n}>0\text{ and }Numerator(\frac{-\ln(a_{n})+2\ln(2)}{\ln(5)})\text{bmod}2=0\text{ and }Denominator(\frac{-\ln(a_{n})+2\ln(2)}{\ln(5)})\text{bmod}2=1$$