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 A121661 #16 Nov 04 2018 03:45:06 %S A121661 1,6,55,556,7839,118141,2488800,54871741,1374282325,35786212191, %T A121661 1182319284628,40234641889543,1409394785418633,53597236487797597, %U A121661 2091701617809524916,96271871655725943733,4719413412748380767833 %N A121661 Duplicate of A118836. %C A121661 Previous name was: Denominator of fraction equal to the continued fraction [4, 6, 9, ..., semiprime(n)]. %C A121661 Numerator of fraction equal to the continued fraction [4, 6, 9, ..., semiprime(n)] is A121660. Hence A121660/A121661 is semiprime analog of A036247/A036248. %F A121661 a(n) = A118836(n). - _Georg Fischer_, Nov 02 2018 %e A121661 a(1) = denominator of 4 = 1. %e A121661 a(2) = denominator of 4 + 1/6 = denominator of 25/6 = 6. %e A121661 a(3) = denominator of 4 + 1/(6+1/9) = denominator of 229/55 = 55. %e A121661 a(10) = denominator of 4+1/(6+1/(9+1/(10+ 1/(14+1/(15+ 1/(21+1/(22+1/(25+1/(26))))))))) = denominator of 149001936472/35786212191 = 35786212191. %p A121661 A121661 := proc(n) local x,i ; x := A001358(n) ; for i from n-1 to 1 by -1 do x := A001358(i)+1/x ; end do: denom(%) ; end proc: # _R. J. Mathar_, Jun 29 2011 %K A121661 dead %O A121661 1,2 %A A121661 _Jonathan Vos Post_, Aug 14 2006