cp's OEIS Frontend

A305980 Filter sequence for a(Squarefree numbers > 1) = constant sequences.

%I A305980 #6 Jul 02 2018 20:25:25
%S A305980 1,2,2,3,2,2,2,4,5,2,2,6,2,2,2,7,2,8,2,9,2,2,2,10,11,2,12,13,2,2,2,14,
%T A305980 2,2,2,15,2,2,2,16,2,2,2,17,18,2,2,19,20,21,2,22,2,23,2,24,2,2,2,25,2,
%U A305980 2,26,27,2,2,2,28,2,2,2,29,2,2,30,31,2,2,2,32,33,2,2,34,2,2,2,35,2,36,2,37,2,2,2,38,2,39,40,41,2,2,2,42,2,2,2,43,2,2,2
%N A305980 Filter sequence for a(Squarefree numbers > 1) = constant sequences.
%C A305980 For all i, j: A305800(i) = A305800(j) => a(i) = a(j).
%H A305980 Antti Karttunen, <a href="/A305980/b305980.txt">Table of n, a(n) for n = 1..100000</a>
%F A305980 a(1) = 1; for n > 1, if A008966(n) = 1 [when n is in A005117], then a(n) = 2, otherwise a(n) = 2+A057627(n).
%o A305980 (PARI)
%o A305980 up_to = 100000;
%o A305980 partialsums(f,up_to) = { my(v = vector(up_to), s=0); for(i=1,up_to,s += f(i); v[i] = s); (v); }
%o A305980 v057627 = partialsums(x -> !issquarefree(x),up_to);
%o A305980 A057627(n) = v057627[n];
%o A305980 A305980(n) = if(1==n,n,if(issquarefree(n),2,2+A057627(n)));
%Y A305980 Cf. A005117, A008966, A057627, A305800.
%K A305980 nonn
%O A305980 1,2
%A A305980 _Antti Karttunen_, Jul 02 2018