A017967 Powers of sqrt(21) rounded down.

1, 4, 21, 96, 441, 2020, 9261, 42439, 194481, 891223, 4084101, 18715701, 85766121, 393029741, 1801088541, 8253624572, 37822859361, 173326116021, 794280046581, 3639848436450, 16679880978201, 76436817165460

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..700

Crossrefs

Cf. A010477 (sqrt(21)).

Programs

Magma

[Floor(Sqrt(21^n)): n in [0..30]]; // Vincenzo Librandi, Jun 24 2011

Mathematica

Floor[(Sqrt[21])^Range[0,30]] (* Harvey P. Dale, May 08 2018 *)

PARI

a(n)=sqrtint(21^n) \\ Charles R Greathouse IV, Nov 18 2011

Formula

a(n) = floor(sqrt(21^n)). - Vincenzo Librandi, Jun 24 2011