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 A061009 #11 Feb 19 2024 10:30:25
%S A061009 -2,-1,0,2,3,3,4,4,4,4,5,5,6,6,6,6,7,7,8,8,8,8,9,9,9,9,9,9,10,10,11,
%T A061009 11,11,11,11,11,12,12,12,12,13,13,14,14,14,14,15,15,15,15,15,15,16,16,
%U A061009 16,16,16,16,17,17,18,18,18,18,18,18,19,19,19,19,20,20,21,21,21,21,21,21,22,22,22,22,23,23,23,23,23,23,24,24,24,24,24
%N A061009 a(n) = -2 + Sum_{j=1..n} (-(n-1)!) mod n.
%F A061009 a(n) = a(n-1) + A061007(n) = A061008(n) - 2. For n > 3, a(n) = pi(n) = A000720(n) where pi(n) is the number of primes less than or equal to n.
%e A061009 a(6)=3 since -2 + (-1 mod 1) + (-1 mod 2) + (-2 mod 3) + (-6 mod 4) + (-24 mod 5) + (-120 mod 6) = -2 + 0 + 1 + 1 + 2 + 1 + 0 = 3.
%Y A061009 Cf. A000040, A000142, A061006, A061007, A061008.
%K A061009 sign
%O A061009 1,1
%A A061009 _Henry Bottomley_, Apr 12 2001