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A182675 a(n) = the smallest n-digit number with exactly 8 divisors, a(n) = 0 if no such number exists. 1
0, 24, 102, 1001, 10002, 100006, 1000002, 10000005, 100000006, 1000000003, 10000000001, 100000000006, 1000000000001, 10000000000001, 100000000000018, 1000000000000002, 10000000000000006, 100000000000000007, 1000000000000000001 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = the smallest n-digit number of the form p^7, p^3*q or p*q*r (p, q, r = distinct primes), a(n) = 0 if no such number exists.

LINKS

Table of n, a(n) for n=1..19.

FORMULA

a(n) = min {10^(n-1) <= k < 10^n : A000005(k)=8} if set is nonempty, else a(n) = 0.

MAPLE

with (numtheory):

a:= proc(n) local k;

     if n<2 then 0

   else for k from 10^(n-1) while tau(k)<>8

        do od; k

     fi

    end:

seq (a(n), n=1..20);

CROSSREFS

Cf. A000005, A182676, A180922.

Sequence in context: A213842 A333033 A269047 * A100155 A304415 A268804

Adjacent sequences:  A182672 A182673 A182674 * A182676 A182677 A182678

KEYWORD

nonn,base

AUTHOR

Jaroslav Krizek, Nov 27 2010

EXTENSIONS

Edited by Alois P. Heinz, Nov 27 2010

STATUS

approved

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Last modified August 13 14:01 EDT 2022. Contains 356091 sequences. (Running on oeis4.)