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A068810 Numbers n such that n and its 10's complement are both squares, i.e., n and 10^k - n (where k is the number of digits in n) are squares. 1

%I

%S 1,9,36,64,100,324,676,900,3600,6400,9216,10000,32400,67600,90000,

%T 99856,123904,360000,640000,876096,921600,1000000,3240000,3968064,

%U 6031936,6760000,9000000,9985600,12390400,28901376,36000000,64000000

%N Numbers n such that n and its 10's complement are both squares, i.e., n and 10^k - n (where k is the number of digits in n) are squares.

%C Terms from V. P. Singh. If k in sequence so is k * 100^m. See A068075 for the smaller of the primitive pairs.

%e 324 = 18^2 is a member as 1000 - 324 = 676 = 26^2.

%t Select[Range[10^4]^2, IntegerQ[Sqrt[10^(IntegerLength[#]) - #]] &] (* _Jayanta Basu_, Aug 05 2013 *)

%Y Cf. A068075.

%K nonn,base

%O 1,2

%A _Amarnath Murthy_, Mar 07 2002

%E Edited and extended by _Robert G. Wilson v_, Mar 20 2002

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Last modified December 14 22:42 EST 2019. Contains 329987 sequences. (Running on oeis4.)