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A210620
Nontrivial solution to x = 2*x^2 - 1 mod 10^n.
1
7, 37, 937, 5937, 35937, 335937, 9335937, 19335937, 319335937, 7319335937, 77319335937, 877319335937, 9877319335937, 89877319335937, 389877319335937, 4389877319335937, 84389877319335937, 384389877319335937, 8384389877319335937, 88384389877319335937
OFFSET
1,1
COMMENTS
The trivial solution is x = 1.
REFERENCES
J. A. H. Hunter, Fun with Figures, Oxford University Press, 1956.
MATHEMATICA
f[n_] := Module[{d}, digs = {7}; Do[d = Select[Range[0, 9], Module[{t}, t = digs~Prepend~#; FromDigits[t] == Mod[2 FromDigits[t]^2 - 1, 10^(Length[digs] + 1)]] &][[1]]; digs = digs~Prepend~d, {n}]; FromDigits[digs]]; Table[f[n - 1], {n, 10}] (* Brenton Bostick, Mar 27 2012 *)
PROG
(PARI) a(n)=lift(chinese(Mod(1, 2^n), Mod(5^n\2, 5^n))) \\ Charles R Greathouse IV, Mar 28 2012
CROSSREFS
Cf. A007185.
Sequence in context: A117731 A155010 A292807 * A250843 A078303 A127729
KEYWORD
base,easy,nonn
AUTHOR
Michael Brundage, Mar 27 2012
STATUS
approved