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.
8 is in the sequence because 8 is in A275608, but none of 1, 2, and 4 are in A275608.
f:= proc(n) local t,r,m;
r:= 1; t:= 1;
for m from 1 do
r:= r*m mod n;
if r = 0 then return 0 fi;
t:= t + r mod n;
if t = 0 then return m+1 fi;
od;
end proc:
f(1):= 1:
map(f, [$1..100]); # Robert Israel, Nov 14 2016
a[n_] := Module[{t, r, m}, r = 1; t = 1; For[m = 1, True, m++, r = Mod[r*m, n]; If[r == 0, Return[0]]; t = Mod[t+r, n]; If[t == 0, Return[m+1]]]];
Array[a, 100] (* Jean-François Alcover, Apr 12 2019, after Robert Israel *)
filter:= proc(n) local t,r,m;
r:= 1; t:= 1;
for m from 1 do
r:= r*m mod n;
if r = 0 then return false fi;
t:= t + r mod n;
if t = 0 then return true fi;
od;
end proc:
filter(1):= true:
select(filter, [$1..1000]); # Robert Israel, Nov 14 2016
okQ[n_] := Module[{t, r, m}, r = 1; t = 1; For[m = 1, True, m++, r = Mod[r*m, n]; If[r == 0, Return[False]]; t = Mod[t + r, n]; If[t == 0, Return[True]]]];
okQ[1] = True;
Select[Range[1000], okQ] (* Jean-François Alcover, Apr 10 2019, after Robert Israel *)
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