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 A088004 #20 May 15 2017 23:38:14
%S A088004 1,1,1,1,1,2,2,2,2,3,3,3,3,4,5,5,5,5,5,5,6,7,7,7,7,8,8,8,8,7,7,7,8,9,
%T A088004 10,10,10,11,12,12,12,11,11,11,11,12,12,12,12,12,13,13,13,13,14,14,15,
%U A088004 16,16,16,16,17,17,17,18,17,17,17,18,17,17,17,17,18,18,18,19,18,18,18,18
%N A088004 "Truncated Mertens function": values of -1 at primes are left out, that is, summatory Moebius when argument runs through nonprimes.
%C A088004 Since the principal source of negative excursions of the Mertens function is here eliminated, most probably this sequence increases ad infinitum albeit non-monotonically; it decreases at squarefree numbers with an odd number of prime divisors, e.g., 30 and 42.
%C A088004 Positions of records of a(n) are in A030229. - _Michael De Vlieger_, May 15 2017
%H A088004 Michael De Vlieger, <a href="/A088004/b088004.txt">Table of n, a(n) for n = 1..10000</a>
%F A088004 a(n) = A002321(n) - (-1)*pi(n) = A002321(n) + A000720(n).
%t A088004 mer[x_] := mer[x-1]+MoebiusMu[x]; mer[0]=0; $RecursionLimit=1000; Table[mer[w]+PrimePi[w], {w, 1, 256}]
%t A088004 (* Second program: *)
%t A088004 Accumulate@ Array[MoebiusMu@ # + Boole[PrimeQ@ #] &, 81] (* _Michael De Vlieger_, May 15 2017 *)
%Y A088004 Cf. A000720, A002321, A008683, A030229.
%K A088004 nonn
%O A088004 1,6
%A A088004 _Labos Elemer_, Oct 14 2003