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 A017919 #41 Jun 19 2024 10:36:27 %S A017919 1,2,5,11,25,55,125,279,625,1397,3125,6987,15625,34938,78125,174692, %T A017919 390625,873464,1953125,4367320,9765625,21836601,48828125,109183006, %U A017919 244140625,545915033,1220703125,2729575167 %N A017919 Powers of sqrt(5) rounded down. %C A017919 a(n) is the total length (rounded down to integer) of the elements of a variant of a 5-element fractal after n iterations, starting with 5 elements, each of whose length is 1/5 (in some units). See illustration in the Links. - _Kival Ngaokrajang_, Feb 26 2015 %H A017919 Vincenzo Librandi, <a href="/A017919/b017919.txt">Table of n, a(n) for n = 0..1000</a> %H A017919 Kival Ngaokrajang, <a href="/A017919/a017919_3.pdf">Illustration of initial terms</a> %t A017919 Floor[(Sqrt[5])^Range[0,40]] (* _Vincenzo Librandi_, Nov 20 2011 *) %o A017919 (PARI) a(n)=sqrtint(5^n) \\ _Charles R Greathouse IV_, Nov 18 2011 %o A017919 (Magma) [Floor(Sqrt(5^n)): n in [0..40]]; // _Vincenzo Librandi_, Nov 20 2011 %o A017919 (Python) %o A017919 from math import isqrt %o A017919 def A017919(n): return isqrt(5**n) # _Chai Wah Wu_, Jun 19 2024 %Y A017919 Cf. A017920, A017921. %K A017919 nonn %O A017919 0,2 %A A017919 _N. J. A. Sloane_