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A182680
a(n) = the largest n-digit number with exactly 10 divisors, a(n) = 0 if no such number exists.
1
0, 80, 976, 9904, 99952, 999952, 9999952, 99999824, 999999536, 9999999824, 99999999536, 999999999567, 9999999999963, 99999999999728, 999999999999856, 9999999999998896, 99999999999999824, 999999999999999952, 9999999999999999856, 99999999999999999568
OFFSET
1,2
COMMENTS
a(n) = the largest n-digit number of the form p^9 or p^4*q (p, q distinct primes), a(n) = 0 if no such number exists.
FORMULA
A000005(a(n)) = 10.
a(n) >= A182679(n).
MATHEMATICA
Table[k=10^n-1; While[k>10^(n-1) && DivisorSigma[0, k] != 10, k--]; If[k==10^(n-1), k=0]; k, {n, 20}]
CROSSREFS
Sequence in context: A052519 A246545 A198400 * A203347 A201193 A264129
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Nov 27 2010
EXTENSIONS
Extended by T. D. Noe, Nov 29 2010
STATUS
approved