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A182672
a(n) = the largest n-digit number with exactly 6 divisors, a(n) = 0 if no such number exists.
1
0, 99, 981, 9981, 99997, 999981, 9999988, 99999961, 999999981, 9999999908, 99999999964, 999999999927, 9999999999884, 99999999999932, 999999999999908, 9999999999999925, 99999999999999963, 999999999999999929, 9999999999999999999, 99999999999999999916
OFFSET
1,2
COMMENTS
a(n) = the largest n-digit number of the form p^5 or p^2*q^1, (p, q = distinct primes), a(n) = 0 if no such number exists.
FORMULA
A000005(a(n)) = 6.
MATHEMATICA
Table[k=10^n-1; While[k>10^(n-1) && DivisorSigma[0, k] != 6, k--]; If[k==10^(n-1), k=0]; k, {n, 20}]
CROSSREFS
Cf. A182671 (smallest n-digit number with exactly 6 divisors).
Sequence in context: A177686 A135219 A108904 * A124113 A223157 A223155
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Nov 27 2010
EXTENSIONS
Extended by T. D. Noe, Nov 29 2010
STATUS
approved