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 A078476 #14 Jun 17 2017 04:00:43 %S A078476 1,2,6,11,16,22,28,35,42,50,58,67,76,86,96,107,118,130,142,155,168, %T A078476 182,196,211,226,242,258,275,292,310,328,347,366,386,406,427,448,470, %U A078476 492,515,538,562,586,611,636,662,688,715,742,770,798,827,856,886,916,947 %N A078476 Time taken to get n people from one side of a bridge to the other where (a) the only flashlight must be carried when crossing; (b) only one or two people may cross at the same time; (c) a pair crosses at the speed of the slowest member; and (d) the k-th person's speed requires k seconds to cross the bridge. %C A078476 Quasipolynomial of order 2. - _Charles R Greathouse IV_, Mar 26 2013 %H A078476 Torsten Sillke, <a href="http://www.mathematik.uni-bielefeld.de/~sillke/PUZZLES/crossing-bridge">Crossing the bridge</a>. %H A078476 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1). %F A078476 For n>1: a(n)=n^2/4+3n-5+((-1)^n-1)/8. %F A078476 G.f.: x*(1+2*x^2+x^3-3*x^4)/((1-x)^3*(1+x)). [_Colin Barker_, Jun 07 2012] %F A078476 Contribution from _Denis Borris_, Mar 26 2013: (Start) %F A078476 n is even: a(n) = (n^2 + 12n - 20) / 4. %F A078476 n is odd : a(n) = (n^2 + 12n - 21) / 4. %F A078476 (End) %e A078476 a(5)=16 since one of the fastest ways is for 1&2 to cross (time 2), 1 to return (1), 4&5 to cross (5), 2 to return (2), 1&3 to cross (3), 1 to return (1) and 1&2 to cross (2) for a total time of 2+1+5+2+3+1+2=16. %o A078476 (PARI) a(n)=n^2\4+3*n-5 \\ _Charles R Greathouse IV_, Mar 26 2013 %K A078476 nonn,easy %O A078476 1,2 %A A078476 _Henry Bottomley_, Jan 03 2003