A343724 a(n) is the smallest n-digit square with all digits even.

0, 64, 400, 4624, 26244, 228484, 2022084, 20268004, 202208400, 2006860804, 20220840000, 200084446864, 2002004266084, 20000286620224, 200080402620484, 2000028662022400, 20000086482842244, 200002866202240000, 2000008648284224400, 20000246442286866064

Offset: 1

Author

Jon E. Schoenfield, May 19 2021

Keywords

• nonn
• base

Comments

From Robert G. Wilson v, May 20 2021: (Start)

The square root of any term is == {0, 2, 8} (mod 10).

Other than 1 and 9, there are no squares which contain only odd digits.

(End)

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..61 (terms for n = 1..40 from Robert G. Wilson v)

Crossrefs

Cf. A030098, A343725.

Programs

Mathematica

a[n_] := Block[{k = Floor[ Sqrt[10^n/5]]}, If[OddQ@k, k--]; While[ Union[ EvenQ[ IntegerDigits[ k^2]]] != {True}, k += 2]; k^2]; Array[ a, 20] (* Robert G. Wilson v, May 20 2021 *)