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 A018036 #15 Sep 05 2025 14:35:04
%S A018036 1,2,7,21,57,159,441,1216,3356,9261,25550,70491,194481,536558,1480323,
%T A018036 4084101,11267724,31086798,85766121,236622224,652822776,1801088541,
%U A018036 4969066719,13709278306,37822859361,104350401110,287894844440,794280046581,2191358423329
%N A018036 Powers of cube root of 21 rounded down.
%H A018036 Vincenzo Librandi, <a href="/A018036/b018036.txt">Table of n, a(n) for n = 0..200</a>
%F A018036 a(n) = floor(21^(n/3)). - _Wesley Ivan Hurt_, Sep 05 2025
%t A018036 Table[Floor[21^(n/3)], {n, 0, 40}] (* _Vincenzo Librandi_, Jan 06 2014 *)
%t A018036 Floor[CubeRoot[21]^Range[0,30]] (* _Harvey P. Dale_, May 25 2025 *)
%o A018036 (Magma) [Floor(21^(n/3)): n in [0..40]]; // _Vincenzo Librandi_, Jan 06 2014
%Y A018036 Cf. powers of cube root of k rounded down: A017979 (k=2), A017982 (k=3), A017985 (k=4), A017988 (k=5), A017991 (k=6), A017994 (k=7), A018000 (k=9), A018003 (k=10), A018006 (k=11), A018009 (k=12), A018012 (k=13), A018015 (k=14), A018018 (k=15), A018021 (k=16), A018024 (k=17), A018027 (k=18), A018030 (k=19), A018033 (k=20), this sequence (k=21), A018039 (k=22), A018042 (k=23), A018045 (k=24).
%K A018036 nonn,changed
%O A018036 0,2
%A A018036 _N. J. A. Sloane_
%E A018036 More terms from _Vincenzo Librandi_, Jan 06 2014