A077486 Largest n-digit square which leaves a square at every step if most significant digit and least significant digit are deleted until a one- or two-digit square is obtained. a(2n) = 0 if no such square exists. a(2n+1) = 9*10^2n only if no nontrivial candidate exists.

9, 81, 841, 8649, 64009, 0, 4004001, 0, 900000000, 0, 40000400001, 0, 9000000000000, 0, 400000040000001, 0, 90000000000000000, 0, 4000000004000000001, 0, 900000000000000000000, 0, 40000000000400000000001

Offset

1,1

Links

Table of n, a(n) for n=1..23.

Formula

Beginning with term a(6) the following pattern applies: a(4k)=0; a(4k+1)=9*10^4k=(3*10^2k)^2; a(4k+2)=0; a(4k+3)=(2*10^(2k+1)+1)^2. - Ray Chandler, Aug 03 2003

Example

a(5) = 64009 as 64009, 400 and 0 all are squares. Though 90000 is a candidate, it is a trivial one.

Crossrefs

Cf. A077485.

Sequence in context: A137062 A001514 A077364 * A233021 A366273 A187122

Adjacent sequences: A077483 A077484 A077485 * A077487 A077488 A077489

Keyword

base,nonn

Author

Amarnath Murthy, Nov 07 2002

Extensions

More terms from Ray Chandler, Aug 03 2003

Status

approved