cp's OEIS Frontend

A116453 Third smallest number with exactly n prime factors.

%I A116453 #16 Apr 18 2025 14:46:14
%S A116453 5,9,18,36,72,144,288,576,1152,2304,4608,9216,18432,36864,73728,
%T A116453 147456,294912,589824,1179648,2359296,4718592,9437184,18874368,
%U A116453 37748736,75497472,150994944,301989888,603979776,1207959552,2415919104
%N A116453 Third smallest number with exactly n prime factors.
%C A116453 Smallest term in A116451 having exactly n prime factors;
%C A116453 a(n) = A116451(A116454(n)) = A116454(n) + 2 * n + 3;
%C A116453 a(n) = A005010(n-2) = 9*2^(n - 2) for n > 1.
%H A116453 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (2).
%e A116453 a(1) =  5 = A000040(3) > A000040(2) =  3 > A000040(1) =  2;
%e A116453 a(2) =  9 = A001358(3) > A001358(2) =  6 > A001358(1) =  4;
%e A116453 a(3) = 18 = A014612(3) > A014612(2) = 12 > A014612(1) =  8;
%e A116453 a(4) = 36 = A014613(3) > A014613(2) = 24 > A014613(1) = 16.
%o A116453 (Python)
%o A116453 def A116453(n): return 9<<n-2 if n>1 else 5 # _Chai Wah Wu_, Aug 23 2024
%K A116453 nonn,easy
%O A116453 1,1
%A A116453 _Reinhard Zumkeller_, Feb 16 2006