cp's OEIS Frontend

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.

A060215 Least a(n) such that the period of continued fraction for sqrt(a(n)) has at least n successive 1's.

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%I A060215 #39 Jul 20 2024 20:43:12
%S A060215 2,3,7,7,13,58,58,135,461,819,2081,13624,13834,35955,95773,244647,
%T A060215 639389,1798800,4374866,11448871,30002701,78439683,205337953,
%U A060215 541653136,1407271538
%N A060215 Least a(n) such that the period of continued fraction for sqrt(a(n)) has at least n successive 1's.
%C A060215 a(25) <= 3684200835. - _Chai Wah Wu_, Jul 20 2024
%e A060215 n  a(n)      C.f. period
%e A060215 0  2          1    2
%e A060215 1  3          2    1,2
%e A060215 2  7          4    1,1,1,4
%e A060215 3  7          4    1,1,1,4
%e A060215 4  13         5    1,1,1,1,6
%e A060215 5  58         7    1,1,1,1,1,1,14
%e A060215 6  58         7    1,1,1,1,1,1,14
%e A060215 7  135        8    1,1,1,1,1,1,1,22
%e A060215 8  461        15   2,8,10,1,1,1,1,1,1,1,1,10,8,2,42
%e A060215 9  819        10   1,1,1,1,1,1,1,1,1,56
%e A060215 10 2081       11   1,1,1,1,1,1,1,1,1,1,90
%e A060215 11 13624      62   1,2,1,...,4,5,1,1,1,1,1,1,1,1,1,1,1,5,4,...,1,2,1,232
%e A060215 12 13834      13   1,1,1,1,1,1,1,1,1,1,1,1,234
%e A060215 13 35955      14   1,1,1,1,1,1,1,1,1,1,1,1,1,378
%e A060215 14 95773      25   2,8,2,8,154,1,1,1,1,1,1,1,1,1,1,1,1,1,1,154,8,2,8,2,618
%e A060215 15 244647     16   1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,988
%e A060215 16 639389     17   1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1598
%e A060215 17 1798800    160  5,5,1,19,...,2,60,(17 1's),60,2,...,19,1,5,5,2682
%e A060215 18 4374866    19   1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,4182
%e A060215 19 11448871   20   1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,6766
%e A060215 20 30002701   35   2,8,2,8,2,8,2738,(20 1's),738,8,2,8,2,8,2,10954
%e A060215 21 78439683   22   1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,17712
%e A060215 22 205337953  23   1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,28658
%e A060215 23 541653136  1442 2,3,1,...,4,581,(23 1's),581,4,...,1,3,2,46546
%e A060215 24 1407271538 25   1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,75026
%t A060215 Table[Block[{k = 2}, While[NoneTrue[Map[Length, Select[If[IntegerQ@ #, {{#}}, Split@ Last@ ContinuedFraction@ #] &@ Sqrt@ k, First@ # == 1 &]], # >= n &], k++]; k], {n, 14}] (* _Michael De Vlieger_, Oct 26 2017 *)
%o A060215 (PARI) print1("2, 3, 7, ");n=3;for(k=1,10^6,v=contfrac(sqrt(k));s=0; for(l=1,length(v)-n,if(v[l]==1,s=s+1,s=0);if(s==n,print1(k", ");n=n+1;k=k-1;break)))
%Y A060215 Cf. A071296.
%K A060215 nonn,more
%O A060215 0,1
%A A060215 _Jeff Burch_, Mar 21 2001
%E A060215 More terms from _Ralf Stephan_, Mar 26 2003
%E A060215 Definition clarified by _T. D. Noe_, Apr 07 2014
%E A060215 a(11), a(14) corrected and a(17)-a(23) added by _Lars Blomberg_, Oct 24 2015
%E A060215 a(0), a(24) from _Chai Wah Wu_, Sep 23 2019