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PERFECT POWERS: PILLAI’S WORKS AND THEIR DEVELOPMENTS
, 2009
"... Abstract. A perfect power is a positive integer of the form ax where a ≥ 1 and x ≥ 2 are rational integers. Subbayya Sivasankaranarayana Pillai wrote several papers on these numbers. In 1936 and again in 1945 he suggested that for any given k ≥ 1, the number of positive integer solutions (a, b, x, y ..."
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Abstract. A perfect power is a positive integer of the form ax where a ≥ 1 and x ≥ 2 are rational integers. Subbayya Sivasankaranarayana Pillai wrote several papers on these numbers. In 1936 and again in 1945 he suggested that for any given k ≥ 1, the number of positive integer solutions (a, b, x, y), with x ≥ 2 and y ≥ 2, to the Diophantine equation ax − by = k is finite. This conjecture amounts to saying that the distance between two consecutive elements in the sequence of perfect powers tends to infinity. After a short introduction to Pillai’s work on Diophantine questions, we quote some later developments and we discuss related open problems.
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, 2009
"... Report on some recent advances in Diophantine approximation Michel Waldschmidt............................................. 1 1 Rational approximation to a real number........................ 5 ..."
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Report on some recent advances in Diophantine approximation Michel Waldschmidt............................................. 1 1 Rational approximation to a real number........................ 5
A NEW ALGORITHM TO SEARCH FOR SMALL NONZERO x 3 − y 2  VALUES
"... Abstract. In relation to Hall’s conjecture, a new algorithm is presented to search for small nonzero k = x 3 −y 2  values. Seventeen new values of k<x 1/2 are reported. 1. Hall’s conjecture Dealing with natural numbers, the difference (1.1) k = x 3 − y 2 is zero when x = t 2 and y = t 3 but, in ..."
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Abstract. In relation to Hall’s conjecture, a new algorithm is presented to search for small nonzero k = x 3 −y 2  values. Seventeen new values of k<x 1/2 are reported. 1. Hall’s conjecture Dealing with natural numbers, the difference (1.1) k = x 3 − y 2 is zero when x = t 2 and y = t 3 but, in other cases, it seems difficult to achieve small absolute values. For a given k ̸ = 0, (1.1), known as Mordell’s equation, is an elliptic curve and has only finitely many solutions in integers by Siegel’s theorem. Therefore, for any nonzero k value, there are only finitely many solutions in x (which is hence bounded). There is a proven lower bound, due to A. Baker [1] and improved by H. M. Stark [14], that places the size of k above the order of log c (x) for any c<1. A bound concerning the minimal growth rate of k  was found early by M. Hall [2, 7] by means of a parametric family of the form (1.2) f(t) = t 9 (t9 +6t 6 +15t 3 + 12), g(t) = t15 27 + t12 +4t9 +8t6 3 f 3 (t) − g2 (t) = − 3t6 +14t3+27