A227043 - OEIS

%I #9 Jul 01 2013 13:24:42

%S 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 100,26,108,56,116,15,124,64,132,34,140,72,148,19,156,80,164,42,172,

%U 88,180,23,188,96,196,50,204,104,212,27,220,112,228,58,236,120

%N Numerator of harmonic mean H(n,2), n>= 0.

%C 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 The corresponding denominator is given in A000265(n+2), n>= 0.

%C a(n+2), n>=0, is the second column (m=2) of the triangle A227041.

%F a(n) = numerator(4*n/(n+2)), n >= 0.

%F a(n) = 4*n/gcd(n+2,4*n) = 4*n/gcd(n+2,8), n >= 0.

%e The rationals H(n,2) begin:

%e 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 Cf. A227041(n+2,2), A000265(n+2) (denominator), n >= 0.

%K nonn,easy,frac

%O 0,2

%A _Wolfdieter Lang_, Jul 01 2013