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 A048862 #18 Sep 03 2024 08:24:59 %S A048862 0,0,1,7,42,338,3242,42324,646021,12283522,300369786,8028642999, %T A048862 259488750732,9414916809082,362597750396726,15397728527812843, %U A048862 742238179058722875,40068968501510691877,2251262473052300960808,139566579945945392719394 %N A048862 Number of primes in the reduced residue system of n-th primorial number (=A002110(n)). %H A048862 Kim Walisch, <a href="https://github.com/kimwalisch/primecount">Fast C++ prime counting function implementation (primecount)</a>. %F A048862 a(n) = A000849(n) - n = A000720(A002110(n)) - A001221(A002110(n)). %e A048862 For n = 3, the 3rd primorial is 30, phi(30) = 8, a(3) = 8-1 = 7 since 1 is nonprime. See A048597. %e A048862 For n = 4, the 4th primorial is 210, the size of its reduced residue system (RRS) is 48 of which 42 are primes and 6 are either composite numbers or 1. %Y A048862 Cf. A000010 (phi), A000720, A000849, A001221, A002110, A007625, A048597, A048863. %K A048862 more,nonn %O A048862 0,4 %A A048862 _Labos Elemer_ %E A048862 a(0) prepended and extended by _Max Alekseyev_, Feb 22 2016 %E A048862 a(17) corrected and a(18)-a(19) calculated using Kim Walisch's primecount and added by _Amiram Eldar_, Sep 03 2024