%I #16 Apr 25 2021 12:18:04
%S 4,25,121,1369,10201,100489,1018081,10004569,100140049,1000267129,
%T 10000600009,100008370081,1000006000009,10000033772089,
%U 100000380000361,1000000025191729,10000001400000049,100000000621806289,1000000014000000049,10000000055856073561
%N a(n) is the smallest n-digit number with 3 divisors.
%F a(n) = A131581(n-1)^2.
%t Table[Prime[1 + PrimePi[Sqrt[10^n]]]^2, {n, 0, 25}] (* _T. D. Noe_, Aug 19 2011 *)
%o (Python)
%o from math import sqrt
%o from sympy import nextprime
%o def a(n): return nextprime(int(sqrt(10**n+1)))**2
%o print([a(n) for n in range(20)]) # _Michael S. Branicky_, Apr 25 2021
%Y Cf. A131581, A132153, A136582, A175734.
%K nonn,base
%O 1,1
%A _Jaroslav Krizek_, Aug 24 2010