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 A333640 #10 Mar 31 2020 06:26:53 %S A333640 421,757,1021,1097,1117,1241,1301,1553,1625,1649,1973,2069,2125,2237, %T A333640 2249,2273,2665,2789,2861,3085,3349,3373,3461,3517,3545,3877,3917, %U A333640 4133,4397,4481,4573,4589,4885,5389,5521,5573,5713,5717,6185,6221,6317,6637,6997,7093 %N A333640 Numbers k such that the continued fraction of (1 + sqrt(k))/2 has period 13. %C A333640 For primes in this sequence see A146358. %H A333640 Amiram Eldar, <a href="/A333640/b333640.txt">Table of n, a(n) for n = 1..10000</a> %e A333640 a(1) = 421 because the continued fraction of (1 + sqrt(421))/2 = 10, 1, 3, 6, 1, 1, 2, 2, 1, 1, 6, 3, 1, 19, 1, 3, 6, ... has a period (1, 3, 6, 1, 1, 2, 2, 1, 1, 6, 3, 1, 19) of length 13. %t A333640 Select[Range[10^4], !IntegerQ @ Sqrt[#] && Length[ContinuedFraction[(1 + Sqrt[#])/2][[2]]] == 13 &] %Y A333640 Cf. A000290, A078370, A146326-A146345, A146348-A146362. %K A333640 nonn %O A333640 1,1 %A A333640 _Amiram Eldar_, Mar 31 2020