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 A048611 Find smallest pair (x,y) such that x^2 - y^2 = 11...1 (n times) = (10^n-1)/9; sequence gives value of x. 2
 1, 6, 20, 56, 156, 340, 2444, 4440, 167000, 55556, 267444, 333400, 132687920, 5555556, 10731400, 40938800, 2682647040, 333334000, 555555555555555556, 3334367856, 11034444280, 35595935980, 5555555555555555555556 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Least solutions for 'Difference between two squares is a repunit of length n'. REFERENCES David Wells, "Curious and Interesting Numbers", Revised Ed. 1997, Penguin Books, p. 119. ISBN 0-14-026149-4. LINKS H. Havermann, Repunit Square Differences (gives many more terms) EXAMPLE For n=2, 6^2 - 5^2 = 11. MATHEMATICA s = Flatten[Table[r = (10^i - 1)/9; d = Divisors[r]; p = d[[Length[d]/2]]; Solve[{x - y == p, x + y == r/p}, {y, x}], {i, 2, 56}]]; Prepend[Cases[s, Rule[x, n_] -> n], 1] CROSSREFS Cf. A048612, A000042, A002275. Sequence in context: A260777 A014480 A048778 * A292480 A200528 A127982 Adjacent sequences:  A048608 A048609 A048610 * A048612 A048613 A048614 KEYWORD nonn,nice AUTHOR EXTENSIONS Corrected and extended by Patrick De Geest, Jun 15 1999 More terms from Hans Havermann, Jul 02 2000 STATUS approved

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Last modified September 26 16:43 EDT 2020. Contains 337374 sequences. (Running on oeis4.)