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 A227043 #9 Jul 01 2013 13:24:42 %S A227043 0,4,2,12,8,20,3,28,16,36,10,44,24,52,7,60,32,68,18,76,40,84,11,92,48, %T A227043 100,26,108,56,116,15,124,64,132,34,140,72,148,19,156,80,164,42,172, %U A227043 88,180,23,188,96,196,50,204,104,212,27,220,112,228,58,236,120 %N A227043 Numerator of harmonic mean H(n,2), n>= 0. %C A227043 a(n) = numerator(H(n,2)) = numerator(4*n/(n+2)), n>=0, with H(n,2) the harmonic mean of n and 2. %C A227043 The corresponding denominator is given in A000265(n+2), n>= 0. %C A227043 a(n+2), n>=0, is the second column (m=2) of the triangle A227041. %F A227043 a(n) = numerator(4*n/(n+2)), n >= 0. %F A227043 a(n) = 4*n/gcd(n+2,4*n) = 4*n/gcd(n+2,8), n >= 0. %e A227043 The rationals H(n,2) begin: %e A227043 0, 4/3, 2, 12/5, 8/3, 20/7, 3, 28/9, 16/5, 36/11, 10/3, 44/13, 24/7, 52/15, 7/2, 60/17, ... %Y A227043 Cf. A227041(n+2,2), A000265(n+2) (denominator), n >= 0. %K A227043 nonn,easy,frac %O A227043 0,2 %A A227043 _Wolfdieter Lang_, Jul 01 2013