Article
Keywords:
Pillai's Diophantine equation; Lehmer sequence; primitive divisor
Summary:
S. S. Pillai proved that for a fixed positive integer $a$, the exponential Diophantine equation $x^y-y^x= a$, $\min (x,y)>1$, has only finitely many solutions in integers $x$ and $y$. We prove that when $a$ is of the form $2z^2$, the above equation has no solution in integers $x$ and $y$ with $\gcd (x,y)=1$.
References:
[9] Pillai, S. S.:
On the indeterminate equation $x^y-y^x = a$. Annamalai Univ. J. 1 (1932), 59-61.
Zbl 0005.05302
[10] Robbins, N.:
Fibonacci numbers of the form $cx^2$, where $1 \leq c \leq 1000$. Fibonacci Q. 28 (1990), 306-315.
MR 1077496 |
Zbl 0728.11013
[12] Waldschmidt, M.:
Perfect powers: Pillai's works and their developments. Collected works of S. Sivasankaranarayana Pillai. Volume 1 Ramanujan Mathematical Society, Mysore (2010), xxii--xlvii.
MR 2766491