Santana and Diaz - Barrero ( 2006 ) proved another identity relating Pell numbers to squares .
Santana and Diaz - Barrero ( 2006 ) showing that the sum of the Pell numbers up to P is always a square :
Santana and Diaz - Barrero ( 2006 ) proved another identity relating Pell numbers to squares and showing that the sum of the Pell numbers up to P is always a square :