login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A182675 a(n) = the smallest n-digit number with exactly 8 divisors, a(n) = 0 if no such number exists. 1

%I #10 Apr 03 2012 14:53:31

%S 0,24,102,1001,10002,100006,1000002,10000005,100000006,1000000003,

%T 10000000001,100000000006,1000000000001,10000000000001,

%U 100000000000018,1000000000000002,10000000000000006,100000000000000007,1000000000000000001

%N a(n) = the smallest n-digit number with exactly 8 divisors, a(n) = 0 if no such number exists.

%C 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.

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

%p with (numtheory):

%p a:= proc(n) local k;

%p if n<2 then 0

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

%p do od; k

%p fi

%p end:

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

%Y Cf. A000005, A182676, A180922.

%K nonn,base

%O 1,2

%A _Jaroslav Krizek_, Nov 27 2010

%E Edited by _Alois P. Heinz_, Nov 27 2010

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)