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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 (list; graph; refs; listen; history; text; internal format)
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.

LINKS

Table of n, a(n) for n=1..25.

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

Adjacent sequences:  A182674 A182675 A182676 * A182678 A182679 A182680

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

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Last modified October 6 19:00 EDT 2022. Contains 357270 sequences. (Running on oeis4.)