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A182677
a(n) = the smallest n-digit number with exactly 9 divisors, a(n) = 0 if no such number exists.
1
0, 36, 100, 1089, 11236, 101761, 1006009, 10023556, 100020001, 1000520161, 10000200001, 100000780441, 1000002000001, 10000021122961, 100000020000001, 1000000341419524, 10000000200000001, 100000004416539529, 1000000012000000036, 10000000017908741569, 100000000060000000009, 1000000000083244219609, 10000000001400000000049, 100000000002632322172441, 1000000000014000000000049
OFFSET
1,2
COMMENTS
a(n) = the smallest n-digit number of the form p^8 or p^2*q^2 (p, q = distinct primes), a(n) = 0 if no such number exists.
FORMULA
A000005(a(n)) = 9.
MATHEMATICA
Table[k=10^(n-1); While[k<10^n && DivisorSigma[0, k] != 9, k++]; If[k==10^n, k=0]; k, {n, 20}]
CROSSREFS
See A182678(n) - the largest n-digit number with exactly 9 divisors.
Sequence in context: A323064 A163246 A014738 * A076768 A282853 A341046
KEYWORD
nonn,base
AUTHOR
Jaroslav Krizek, Nov 27 2010
EXTENSIONS
Extended by T. D. Noe, Nov 29 2010
a(11)-a(25) from Robert Gerbicz, Nov 29 2010
STATUS
approved