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 A380117 #10 Jan 31 2025 07:19:53
%S A380117 0,1,2,1,2,2,3,2,0,0,1,1,2,2,2,1,2,2,3,3,3,3,4,4,0,0,-2,-2,-1,-1,0,-1,
%T A380117 -1,-1,-1,-1,0,0,0,0,1,1,2,2,2,2,3,3,-3,-3,-3,-3,-2,-2,-2,-2,-2,-2,-1,
%U A380117 -1,0,0,0,-1,-1,-1,0,0,0,0,1,1,2,2,2,2,2,2,3
%N A380117 a(n) = n - A380118(n).
%C A380117 Conjecture: The sign of the terms changes infinitely often.
%H A380117 Peter Luschny, <a href="/A380117/b380117.txt">Table of n, a(n) for n = 1..20000</a>
%p A380117 ExpLambda := n -> n / ilcm(op(numtheory[divisors](n) minus {1, n})):
%p A380117 A380118 := proc(n) option remember; ifelse(n = 1, 1,
%p A380117 A380118(n-1) + ExpLambda(n) - ifelse(isprime(n), n, 0)) end:
%p A380117 a := n -> n - A380118(n): seq(a(n), n = 1..79);
%Y A380117 Cf. A380118, A182936.
%K A380117 sign
%O A380117 1,3
%A A380117 _Peter Luschny_, Jan 30 2025