015.13. a) a n = 1 n+5 ;

15.13. а) $$ a_n = \frac{1}{n+5} $$

1. n = 1; $$ a_1 = \frac{1}{1+5} = \frac{1}{6} $$


2. n = 2; $$ a_2 = \frac{1}{2+5} = \frac{1}{7} $$


3. n = 3; $$ a_3 = \frac{1}{3+5} = \frac{1}{8} $$


4. n = 4; $$ a_4 = \frac{1}{4+5} = \frac{1}{9} $$


5. n = 5; $$ a_5 = \frac{1}{5+5} = \frac{1}{10} $$

Ответ: $$\frac{1}{6}; \frac{1}{7}; \frac{1}{8}; \frac{1}{9}; \frac{1}{10} $$.