[Euler-Fermat]

1. $3a^2-2a+10 = (3a+4)(a-2)+18 $
$\therefore a-2\mid 18 $
$a-2 = \pm 1,2,3,6,9,18 $
$a= 3,4,5,8,11,20 $
ผลบวกสมาชิกของ$ a = 51$