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%I #9 Apr 15 2019 16:22:45
%S 0,1,4,9,21,100,400,561,900,2100,8821,10000,11221,17821,40000,56100,
%T 73221,90000,210000,211201,518041,882100,1000000,1001614,1002621,
%U 1012021,1012224,1122100,1302801,1782100,4000000,5012214,5610000
%N Replacing digits d in decimal expansion of n with d^3 yields a square.
%e E.g. 518041 = (5)(1)(8)(0)(4)(1) -> (125)(1)(512)(0)(64)(1) = 12515120641 = 111871^2 and a square.
%t Select[Range[0,561*10^4],IntegerQ[Sqrt[FromDigits[Flatten[ IntegerDigits/@ (IntegerDigits[ #]^3)]]]]&] (* _Harvey P. Dale_, Apr 15 2019 *)
%o (PARI) ccd(n) = {if (n==0, return(0)); my(d = digits(n)); my(nd = ""); for (i=1, #d, nd = Str(nd, d[i]^3);); eval(nd);}
%o isok(n) = issquare(ccd(n)); \\ _Michel Marcus_, Oct 19 2016
%Y Cf. A048390, A048392.
%K nonn,base
%O 1,3
%A _Patrick De Geest_, Mar 15 1999
%E Offset corrected by _Michel Marcus_, Oct 19 2016
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