This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A017967 #17 Sep 08 2022 08:44:43 %S A017967 1,4,21,96,441,2020,9261,42439,194481,891223,4084101,18715701, %T A017967 85766121,393029741,1801088541,8253624572,37822859361,173326116021, %U A017967 794280046581,3639848436450,16679880978201,76436817165460 %N A017967 Powers of sqrt(21) rounded down. %H A017967 Vincenzo Librandi, <a href="/A017967/b017967.txt">Table of n, a(n) for n = 0..700</a> %F A017967 a(n) = floor(sqrt(21^n)). - _Vincenzo Librandi_, Jun 24 2011 %t A017967 Floor[(Sqrt[21])^Range[0,30]] (* _Harvey P. Dale_, May 08 2018 *) %o A017967 (Magma) [Floor(Sqrt(21^n)): n in [0..30]]; // _Vincenzo Librandi_, Jun 24 2011 %o A017967 (PARI) a(n)=sqrtint(21^n) \\ _Charles R Greathouse IV_, Nov 18 2011 %Y A017967 Cf. A010477 (sqrt(21)). %K A017967 nonn %O A017967 0,2 %A A017967 _N. J. A. Sloane_