|
%I #10 Nov 01 2022 13:41:03
%S 1,2,3,1,4,5,6,1,1,7,8,2,9,10,11,1,12,2,13,3,14,15,16,2,1,17,1,4,18,
%T 19,20,1,21,22,23,1,24,25,26,3,27,28,29,5,3,30,31,2,1,2,32,6,33,2,34,
%U 4,35,36,37,7,38,39,4,1,40,41,42,8,43,44,45,1,46,47,3,9,48,49,50,3
%N a(n) is the number of j in the range 1 <= j <= n such that j / rad(j) = n / rad(n).
%H Michel Marcus, <a href="/A357241/b357241.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = |{j <= n : A003557(j) = A003557(n)}|.
%t Table[Length[Select[Range[n], #/Last[Select[Divisors[#], SquareFreeQ]] == n/Last[Select[Divisors[n], SquareFreeQ]] &]], {n, 1, 80}]
%o (PARI) f(n) = n/factorback(factor(n)[, 1]); \\ A003557
%o a(n) = my(x=f(n)); sum(j=1, n, f(j) == x); \\ _Michel Marcus_, Sep 20 2022
%Y Cf. A001694 (positions of 1's), A003557, A008479.
%K nonn
%O 1,2
%A _Ilya Gutkovskiy_, Sep 19 2022
|
