abcd+abc+ab+a=8502
numerele sunt scrise in baza 10; de ex 754=7·100+5·10+4
a,b,c,d<10; (abcd=1000a+100b+10c+d)
=> (1000a+100b+10c+d)+(100a+10b+c)+(10a+b)+a=8502
1111a + 111b + 11c +d =8502
a=7; nu poate fi 8 pt ca 1111·8=8888
a nu poate fi 6 pt ca b,c,d <10
=> 111b+11c+d=8502-7777
111b+11c+d=725
=> b=6
11c+d=725-666
11c+d=59
=>c=5
d=59-55
d=4
a=7, b=6, c=5, d=4
verificare: 7654+765+76+7=8502
