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