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 A159553 #18 Feb 06 2019 00:30:25
%S A159553 2,6,12,28,40,144,140,536,864,2560,2068,12720,8216,45192,78660,182832,
%T A159553 131104,933984,524324,3698240,4890648,13345816,8388652,67390464,
%U A159553 60129600,225470544,279938160,1032462256,536870968,5018059200
%N A159553 a(n) = Sum_{k=0..n} binomial(n,k) * gcd(n,k).
%C A159553 For the purpose of this sequence, gcd(n,0) = n, for all positive integers n.
%C A159553 a(n) is a multiple of n, for all nonnegative integers n.
%H A159553 Michael De Vlieger, <a href="/A159553/b159553.txt">Table of n, a(n) for n = 1..3317</a>
%F A159553 a(n) = A159068(n) + n.
%F A159553 a(n) = 2^n * Sum_{d|n} (phi(d)/d) * Sum_{k=1..d} (-1)^(k*n/d)*cos(k*Pi/d)^n.
%p A159553 A159553 := proc(n) add(binomial(n, k)*gcd(k, n), k=0..n) ; end: seq(A159553(n),n=1..40) ; # _R. J. Mathar_, Apr 29 2009
%t A159553 Table[Sum[Binomial[n, k] GCD[n, k], {k, 0, n}], {n, 30}] (* _Michael De Vlieger_, Oct 30 2017 *)
%Y A159553 Cf. A159068, A159554.
%K A159553 nonn
%O A159553 1,1
%A A159553 _Leroy Quet_, Apr 14 2009
%E A159553 Extended by _R. J. Mathar_, Apr 29 2009
%E A159553 Ambiguous term a(0) removed by _Max Alekseyev_, Jan 09 2015