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a(n) is the n-th number to have n distinct prime factors.
6

%I #19 Jan 09 2021 17:57:11

%S 2,10,60,420,4290,53130,903210,17687670,406816410,11125544430,

%T 338431883790,11833068917670,457077357006270,20384767656323070,

%U 955041577211912190,49230430891074322890,2740956243836856315270,168909608387276001835590,11054926927790884163355330

%N a(n) is the n-th number to have n distinct prime factors.

%H David A. Corneth, <a href="/A073329/b073329.txt">Table of n, a(n) for n = 1..350</a> (terms <= 10^1000)

%F A001221(a(n)) = n <= A001222(a(n)). - _Alois P. Heinz_, Jan 09 2021

%e a(1) = 2 because 2 is the first number to have one prime factor.

%e a(2) = 10 because 10 is the second number to have two prime factors; 6 is the first.

%e a(3) = 60 = 2*2*3*5 because 60 is the third number to have three prime factors (2,3,5); 30 is the first and 42 is the second.

%Y a(n) is last term in n-th row of A048692.

%Y Cf. A001221, A001222, A340467.

%K nonn

%O 1,1

%A _Robert G. Wilson v_, Aug 22 2002

%E Edited by _Dean Hickerson_, Nov 03 2002

%E More terms from _Sascha Kurz_, Jan 03 2003

%E Corrected from a(9) onwards by _T. D. Noe_, Dec 01 2004

%E More terms from _David A. Corneth_, Jan 09 2021