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.
Fifth term of A056855 is 50 and 50 is divisible by 5^2. So 5 is included.
a(6) = 2*(1 + 1/5)*1*5/(6*2) = 1.
f[n_] := Block[{k = Select[Range[n], GCD[ #, n] == 1 &]}, 2Plus @@ (Times @@ k*Plus @@ 1/k)/EulerPhi[n]/n]; Table[ f[n], {n, 26}] (* Robert G. Wilson v, Nov 16 2004 *)
a(8) = (1 + 1/3)*1*3 = 4 because 1 and 3 are those positive integers <= 8/2 and coprime to 8.
b:=proc(n) local B,k: B:={}: for k from 1 to n/2 do if gcd(k,n)=1 then B:=B union {k} else B:=B fi od end: a:=proc(n) add(1/b(n)[j],j=1..nops(b(n)))*product(b(n)[j],j=1..nops(b(n))) end: seq(a(n),n=2..40); # Emeric Deutsch, Apr 22 2006
# second Maple program:
a:= n-> (l-> mul(i, i=l)*add(1/i, i=l))(
select(x-> igcd(x, n)=1, [$1..n/2])):
seq(a(n), n=2..40); # Alois P. Heinz, May 22 2015
a[n_] := Module[{r = Range[Floor[n/2]], s}, s = Select[r, GCD[#, n]==1&]; Total[1/s] Times @@ s];
a /@ Range[2, 40] (* Jean-François Alcover, Nov 18 2020 *)
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