%I
%S 0,99,981,9981,99997,999981,9999988,99999961,999999981,9999999908,
%T 99999999964,999999999927,9999999999884,99999999999932,
%U 999999999999908,9999999999999925,99999999999999963,999999999999999929,9999999999999999999,99999999999999999916
%N a(n) = the largest ndigit number with exactly 6 divisors, a(n) = 0 if no such number exists.
%C a(n) = the largest ndigit number of the form p^5 or p^2*q^1, (p, q = distinct primes), a(n) = 0 if no such number exists.
%F A000005(a(n)) = 6.
%t Table[k=10^n1; While[k>10^(n1) && DivisorSigma[0, k] != 6, k]; If[k==10^(n1), k=0]; k, {n, 20}]
%Y Cf. A182671 (smallest ndigit number with exactly 6 divisors).
%K nonn,base
%O 1,2
%A _Jaroslav Krizek_, Nov 27 2010
%E Extended by _T. D. Noe_, Nov 29 2010
