A035071 a(n) = ceiling(sqrt(4*10^n)).

2, 7, 20, 64, 200, 633, 2000, 6325, 20000, 63246, 200000, 632456, 2000000, 6324556, 20000000, 63245554, 200000000, 632455533, 2000000000, 6324555321, 20000000000, 63245553204, 200000000000, 632455532034, 2000000000000

Offset: 0

Author

Patrick De Geest, Nov 15 1998

Keywords

• nonn
• base

Comments

Previous name: "a(n) is root of square starting with digit 4: first term of runs."

Crossrefs

Cf. A067474 (squares), A035076 (2..9).

Programs

Mathematica

Table[Ceiling @ Sqrt[4 * 10^n], {n, 0, 24}] (* Amiram Eldar, Oct 08 2019 *)