A048391 Replacing digits d in decimal expansion of n with d^3 yields a square.

0, 1, 4, 9, 21, 100, 400, 561, 900, 2100, 8821, 10000, 11221, 17821, 40000, 56100, 73221, 90000, 210000, 211201, 518041, 882100, 1000000, 1001614, 1002621, 1012021, 1012224, 1122100, 1302801, 1782100, 4000000, 5012214, 5610000

Offset

1,3

Links

Table of n, a(n) for n=1..33.

Example

E.g. 518041 = (5)(1)(8)(0)(4)(1) -> (125)(1)(512)(0)(64)(1) = 12515120641 = 111871^2 and a square.

Mathematica

Select[Range[0, 561*10^4], IntegerQ[Sqrt[FromDigits[Flatten[ IntegerDigits/@ (IntegerDigits[ #]^3)]]]]&] (* Harvey P. Dale, Apr 15 2019 *)

Prog

(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); }
isok(n) = issquare(ccd(n)); \\ Michel Marcus, Oct 19 2016

Crossrefs

Cf. A048390, A048392.

Sequence in context: A243640 A243634 A076861 * A343322 A041743 A041943

Adjacent sequences: A048388 A048389 A048390 * A048392 A048393 A048394

Keyword

nonn,base

Author

Patrick De Geest, Mar 15 1999

Extensions

Offset corrected by Michel Marcus, Oct 19 2016

Status

approved