Răspuns :

abcdab=patrat perfect; ab=2•cd

abcdab=ab•10000+cd•100+ab

=10001•ab+100•cd

=10001•2•cd+100•cd

=20102•cd

=2•19•23²•cd

2•19•23²•cd= patrat perfect=> cd=2•19=38 => ab=2•38=76

abcdab=763876

abcdab=(2•19•23)²=874², patrat perfect