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%I #5 Nov 18 2021 11:50:46
%S 1,6,36,91,2775,3916,8911,394716,785631,889111,961191,1456071,5539456,
%T 7704775,13825911,39502716,56440000,76156311,88891111,1507087351,
%U 1764981991,2530200816,2743515775,3950582716,5119859836,5468017600
%N Triangular numbers whose 10's complements are squares.
%e a(5)=2775 because 10^4 - 2775 = 7225 = 85^2.
%t Select[Accumulate[Range[110000]],IntegerQ[Sqrt[10^IntegerLength[#]-#]]&] (* _Harvey P. Dale_, Nov 18 2021 *)
%K base,easy,nonn
%O 1,2
%A _Jason Earls_, Jul 24 2005