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Pillai's Conjecture

open

Posed by S. S. Pillai · combinatorial number theory · ~1 min read · difficulty 4/5

exponential-diophantine

The problem

Pillai's conjecture: for each fixed \(k \geq 1\), there are only finitely many pairs of perfect powers differing by \(k\) — equivalently, the gap between consecutive perfect powers tends to infinity. (Catalan–Mihăilescu is \(k = 1\): the unique consecutive pair is \(8, 9\).)

History & significance

Pillai conjectured it in the 1930s from tables of small perfect powers: gaps grow, but does the growth ever stall? Catalan's theorem (Mihăilescu 2002) is the case of gap 1 — the only consecutive powers are 8 and 9. Lebesgue–Nagell-type results handle fixed exponents; the full conjecture, with both bases and exponents varying, is untouched, and abc would imply it quantitatively.

Still open.

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