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 A017921 #30 Jun 19 2024 10:36:18 %S A017921 1,3,5,12,25,56,125,280,625,1398,3125,6988,15625,34939,78125,174693, %T A017921 390625,873465,1953125,4367321,9765625,21836602,48828125,109183007, %U A017921 244140625,545915034,1220703125,2729575168 %N A017921 Powers of sqrt(5) rounded up. %H A017921 Vincenzo Librandi, <a href="/A017921/b017921.txt">Table of n, a(n) for n = 0..1000</a> %e A017921 sqrt(5)^3 = 11.18033988749895... so a(3) = 12. %e A017921 sqrt(5)^4 = 25, so a(4) = 25. %e A017921 sqrt(5)^5 = 55.90169943749474241... so a(5) = 56. %t A017921 Ceiling[Sqrt[5]^Range[0, 40]] (* _Vincenzo Librandi_, Nov 20 2011 *) %o A017921 (Magma) [Ceiling(Sqrt(5^n)): n in [0..40]]; // _Vincenzo Librandi_, Nov 20 2011 %o A017921 (PARI) a(n) = ceil(sqrt(5^n)); \\ _Michel Marcus_, Dec 14 2017 %o A017921 (Python) %o A017921 from math import isqrt %o A017921 def A017921(n): return isqrt(5**n)+(n&1) # _Chai Wah Wu_, Jun 19 2024 %Y A017921 Cf. A017919, A017920. %K A017921 nonn,easy %O A017921 0,2 %A A017921 _N. J. A. Sloane_