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A076427 Number of solutions to Pillai's equation a^x - b^y = n, with a>0, b>0, x>1, y>1. 4
1, 1, 2, 3, 2, 0, 5, 3, 4, 1, 4, 2, 3, 0, 3, 3, 7, 3, 5, 2, 2, 2, 4, 5, 2, 3, 3, 7, 1, 1, 2, 4, 2, 0, 3, 2, 3, 1, 4, 4, 3, 0, 1, 3, 4, 1, 6, 4, 3, 0, 2, 1, 2, 2, 3, 4, 3, 0, 1, 4, 2, 0, 4, 4, 4, 0, 2, 5, 2, 0, 4, 4, 6, 2, 3, 3, 2, 0, 4, 4, 4, 0, 2, 2, 2, 0, 3, 3, 6, 0, 3, 4, 4, 2, 4, 5, 3, 2, 4, 10 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

This is the classic Diophantine equation of S. S. Pillai, who conjectured that there are only a finite number of solutions for each n. A generalization of Catalan's conjecture that a^x-b^y=1 has only one solution. For n <=100, a total of 274 solutions were found for perfect powers less than 10^12. No additional solutions were found for perfect powers < 10^18.

REFERENCES

R. K. Guy, Unsolved Problems in Number Theory, D9.

T. N. Shorey and R. Tijdeman, Exponential Diophantine Equations, Cambridge University Press, 1986.

LINKS

Table of n, a(n) for n=1..100.

T. D. Noe, Solutions to Pillai's Equation for n<=100

M. A. Bennett, On some exponential equations of S. S. Pillai, Canad. J. Math. 53 (2001), 897-922.

Eric Weisstein's World of Mathematics, Pillai's Conjecture

EXAMPLE

a(4)=3 because there are 3 solutions: 4 = 2^3 - 2^2 = 6^2 - 2^5 = 5^3 - 11^2.

CROSSREFS

Cf. A189117, A001597, A074981.

Sequence in context: A056888 A111182 A178142 * A011024 A105855 A152954

Adjacent sequences:  A076424 A076425 A076426 * A076428 A076429 A076430

KEYWORD

hard,nonn

AUTHOR

T. D. Noe, Oct 11 2002

STATUS

approved

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Last modified December 21 10:06 EST 2014. Contains 252304 sequences.