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 A140481 #4 Mar 31 2012 14:43:40 %S A140481 1,3,8,20,46,96,204,420,864,1752,3520,7068,14160,28360,56736,113508, %T A140481 227040,454176,908424,1816944,3633908,7267828,14535662,29071328, %U A140481 58142704,116285418,232570884,465141864,930283760,1860567600 %N A140481 a(1) = 1; for n >= 1, a(n+1) is obtained by adding to a(n) the a(n)-th smallest number not dividing a(n). %F A140481 a(n+1) = 2*a(n) + tau(a(n)) (cf. A000005). - Hans Havermann and Franklin T. Adams-Watters, Jun 25 2008. Using a(n+1) = a(n) + tau(a(n)) would give A064491. %e A140481 The smallest number not dividing 1 is 2, so a(2) = 1+2 = 3. %e A140481 The numbers not dividing 3 are 2, 4, 5, 6, ..., so a(3) = 3+5 = 8. %e A140481 The numbers not dividing 8 are 3, 5, 6, 7, 9, 10, 11, 12, ..., so a(4) = 8+12 = 20. %Y A140481 Cf. A000005, A064491, A140482. %K A140481 nonn %O A140481 1,2 %A A140481 _Eric Angelini_, Jun 25 2008 %E A140481 More terms from _Hans Havermann_, Jun 25 2008