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 A048980 #11 May 09 2017 08:04:11
%S A048980 1,1,0,-6,-36,-196,-724,7512,366838,11928316,421130508,14598816402,
%T A048980 584642184936,25314953837836,1128885572358548,54492272309366314,
%U A048980 2950485568862138250,213151926413154110951
%N A048980 Difference between number of nonprimes and primes in reduced residue system of primorial numbers.
%F A048980 a(n) = A048863(n) - A048862(n) = A048866(A002110(n)).
%F A048980 a(n) = A005867(n) - 2*A000849(n) + 2*n.
%e A048980 n=4, Q(4)=2*3*5*7=210, reduced residue system includes 48 terms:42 primes and 6 composites and 1: a(4)=6-42=-36.
%t A048980 Table[Function[P, EulerPhi@ P - 2 # &[PrimePi@ P - n]]@ Product[Prime@ i, {i, n}], {n, 0, 12}] (* _Michael De Vlieger_, May 08 2017 *)
%Y A048980 Cf. A048868, A048867, A048597, A002110, A048862, A048863, A048866.
%K A048980 sign
%O A048980 0,4
%A A048980 _Labos Elemer_
%E A048980 Corrected and extended by _Max Alekseyev_, Feb 22 2016