30 x 31 x 32 x.....................x 39 x 40 chia hết cho 7
111 chia hết cho 7
=> 30 x 31 x 32 x.....................x 39 x 40 + 111 chia hết cho 7
Ta có: 30x31x32x…x39x40+111
= 30x31x…x36x38x…x40x37+3x37
=(30x31x…x36x38x…x30+3)x37
Vậy 30x31x32x…x39x40+111 chia hết cho 37