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 A211306 #21 Sep 19 2019 19:48:22
%S A211306 1,2,5,3,13,15,47,53,55,29,74,163,331,341,89,371,1499,513,4657,4837,
%T A211306 4957,5029,55679,59639,12007,12139,12227,12491,87833,90605,454873,
%U A211306 461803,467347,117703,59429,30292,121553,122323,61739,126943,254579,259199,259859
%N A211306 Numerator of Sum_{k=1..n} 1/lambda(k), where lambda(k) is the Carmichael's lambda function.
%H A211306 Amiram Eldar, <a href="/A211306/b211306.txt">Table of n, a(n) for n = 1..10000</a>
%e A211306 1, 2, 5/2, 3, 13/4, 15/4, 47/12, 53/12, 55/12, 29/6, 74/15, 163/30, ...
%p A211306 with(numtheory): a:=n->numer(sum(1/lambda(k), k=1..n)): seq(a(n), n=1..50);
%t A211306 Numerator[Table[Sum[1/CarmichaelLambda[k],{k,1,n}],{n,1,50}]]
%t A211306 Numerator @ Accumulate @ Table[1 / CarmichaelLambda[n], {n, 1, 50}] (* _Amiram Eldar_, Sep 19 2019 *)
%Y A211306 Cf. A002322, A028415, A212716 (denominator).
%K A211306 nonn,frac
%O A211306 1,2
%A A211306 _Michel Lagneau_, May 25 2012