|
%I #14 Apr 02 2022 10:26:11
%S 0,0,0,0,0,1,0,0,0,1,0,1,0,1,1,0,0,2,0,1,1,1,0,1,0,1,0,1,0,1,0,0,1,1,
%T 1,2,0,1,1,1,0,1,0,1,1,1,0,1,0,2,1,1,0,3,1,1,1,1,0,1,0,1,1,0,1,1,0,1,
%U 1,1,0,2,0,1,2,1,1,1,0,1,0,1,0,1,1,1,1,1,0,2,1,1,1,1,1,1,0,2,1,2,0,1,0,1,1,1,0,3
%N a(n) is the exponent of the second smallest prime factor of n, or 0 if n is a power of a prime.
%H Antti Karttunen, <a href="/A351563/b351563.txt">Table of n, a(n) for n = 1..65537</a>
%F a(n) = A067029(A028234(n)).
%e For n = 4 = 2^2 there is no second smallest prime factor as 4 is a power of prime, therefore a(4) = 0.
%e For n = 18 = 2^1 * 3^2, the exponent of the second smallest prime factor (3) is 2, therefore a(18) = 2.
%t Array[If[Length[#] < 2, 0, #[[2, -1]]] &@ FactorInteger[#] &, 108] (* _Michael De Vlieger_, Apr 01 2022 *)
%o (PARI) A351563(n) = if(1>=omega(n), 0, (factor(n))[2,2]);
%Y Cf. A000961 (positions of zeros), A001221, A028234, A067029.
%Y Cf. also A119288, A351567.
%K nonn
%O 1,18
%A _Antti Karttunen_, Apr 01 2022
|
