Răspuns:
n - impar
[tex] {13}^{2k + 1} = 13 \times {13}^{2k} = (4 + 9) \times {13}^{2k} = 4 \times {13}^{2k} + 9 \times {13}^{2k} = (2 \times {13}^{k} ) ^{2} + {(3 \times {13}^{k} })^{2} [/tex]
n - par
[tex] {13}^{2k + 2} = {13}^{2} \times {13}^{2k} = (144 + 25) \times {13}^{2k} = {(12 \times {13}^{k} )}^2 + {(5 \times {13}^{k}) }^{2} [/tex]
