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Squarefree numbers m such that the equation x^2 == m (mod 10^k) has solutions for all k > 0.
1

%I #8 Aug 20 2023 16:56:08

%S 41,89,129,161,201,209,241,249,281,321,329,401,409,449,481,489,521,

%T 561,569,601,609,641,649,681,689,721,761,769,809,849,881,889,921,929,

%U 969,1001,1009,1041,1049,1081,1121,1129,1169,1201,1209,1241,1249,1281,1289

%N Squarefree numbers m such that the equation x^2 == m (mod 10^k) has solutions for all k > 0.

%C The minimal solutions for m=41 are in sequence A187719.

%t Rest[Select[Union[Mod[Range[10000]^2, 10000]], OddQ[#] && SquareFreeQ[#] &]]

%K nonn

%O 1,1

%A _T. D. Noe_, Mar 23 2011