MMMM+
NNNN
OOOO
MNNNO
Observam ca M+N=10
1+O=N
M=1 => N=8=>O=8 =>
1111+
9999
8888
19998
_________________________________________________________________
RRRR x
RRR
OOOO
OOOO
OOOO
OMTRWO
Observam ca R² <10 => R∈{2,3}
Daca R=3 OMTRWO ar avea 7 cifre iar r=8≠3
=> R=2 => O=4 :
2222 x
222
4444
4444
4444
493284