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 A065180 #16 Apr 14 2025 07:39:59
%S A065180 1,4,20,90,420,1910,8820,40590,187880,871494,4057620,18945960,
%T A065180 88738020,416787030,1962922276,9268287390,43868210820,208109782580,
%U A065180 989400443220,4713395564772,22497100553820,107572434560790,515241748300020
%N A065180 Number of site swap patterns with 4 balls and exact period n.
%H A065180 G. C. Greubel, <a href="/A065180/b065180.txt">Table of n, a(n) for n = 1..1000</a>
%H A065180 Juggling Information Service, <a href="http://www.juggling.org/bin/mfs/JIS/help/siteswap/">Site Swap FAQs</a>
%F A065180 G.f.: Sum_{k>=1} mu(k) * log(1 + x^k/(1 - 5*x^k))/k. - _Seiichi Manyama_, Apr 14 2025
%p A065180 [seq(DistSS(p,4),p=1..60)];
%p A065180 A065180 := proc(n)
%p A065180 add( mobius(n/d)*(5^d-4^d),d=numtheory[divisors](n)) /n ;
%p A065180 end proc:
%p A065180 seq(A065180(n),n=1..30) ; # _R. J. Mathar_, Aug 05 2015
%t A065180 a[n_] := DivisorSum[n, MoebiusMu[n/#]*(5^# - 4^#)&]/n; Array[a, 25] (* _Jean-François Alcover_, Mar 06 2016 *)
%Y A065180 Row 4 of A065177.
%Y A065180 Cf. A008683, A065178, A065179.
%K A065180 nonn
%O A065180 1,2
%A A065180 _Antti Karttunen_, Oct 19 2001