Among the states that start with letter A and attained a national sector average of 16.5, give the number of degree-seeking students in the cohort of those students in 2012 .
state that starts with letter A refers to state LIKE 'A%'; national sector average of 16.5 refers to awards_per_natl_value = 16.5; number of degree-seeking students in the cohort refers to grad_cohort; in 2012 refers to year = '2012';
SELECT SUM(T2.grad_cohort) FROM state_sector_details AS T1 INNER JOIN state_sector_grads AS T2 ON T2.stateid = T1.stateid WHERE T2.state LIKE 'A%' AND T1.awards_per_natl_value = 16.5 AND T2.year = 2012