This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A048391 #9 Apr 15 2019 16:22:45
%S A048391 0,1,4,9,21,100,400,561,900,2100,8821,10000,11221,17821,40000,56100,
%T A048391 73221,90000,210000,211201,518041,882100,1000000,1001614,1002621,
%U A048391 1012021,1012224,1122100,1302801,1782100,4000000,5012214,5610000
%N A048391 Replacing digits d in decimal expansion of n with d^3 yields a square.
%e A048391 E.g. 518041 = (5)(1)(8)(0)(4)(1) -> (125)(1)(512)(0)(64)(1) = 12515120641 = 111871^2 and a square.
%t A048391 Select[Range[0,561*10^4],IntegerQ[Sqrt[FromDigits[Flatten[ IntegerDigits/@ (IntegerDigits[ #]^3)]]]]&] (* _Harvey P. Dale_, Apr 15 2019 *)
%o A048391 (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 A048391 isok(n) = issquare(ccd(n)); \\ _Michel Marcus_, Oct 19 2016
%Y A048391 Cf. A048390, A048392.
%K A048391 nonn,base
%O A048391 1,3
%A A048391 _Patrick De Geest_, Mar 15 1999
%E A048391 Offset corrected by _Michel Marcus_, Oct 19 2016