login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A088433 Number of ways to write n as n = u*v*w with 1<=u<=v<w. 6

%I

%S 0,1,1,1,1,2,1,2,1,2,1,4,1,2,2,3,1,3,1,4,2,2,1,6,1,2,2,4,1,5,1,4,2,2,

%T 2,7,1,2,2,6,1,5,1,4,4,2,1,8,1,3,2,4,1,6,2,6,2,2,1,10,1,2,4,5,2,5,1,4,

%U 2,5,1,11,1,2,3,4,2,5,1,9,3,2,1,10,2,2,2,6,1,10,2,4,2,2,2,12,1,3,4,6

%N Number of ways to write n as n = u*v*w with 1<=u<=v<w.

%C a(n) = 1 iff n prime or n prime^2: a(A000430(n))=1.

%H Antti Karttunen, <a href="/A088433/b088433.txt">Table of n, a(n) for n = 1..2048</a>

%e n=12: (1,1,12), (1,2,6), (1,3,4), (2,2,3): therefore a(12)=4;

%e n=18: (1,1,18), (1,2,9), (1,3,6): therefore a(18)=3.

%o (PARI) A088433(n) = { my(s=0); fordiv(n, u, for(v=u, n-1, for(w=v+1, n, if(u*v*w==n, s++)))); (s); }; \\ _Antti Karttunen_, Aug 24 2017

%Y Cf. A034836, A088432, A088434, A122179, A122180.

%K nonn

%O 1,6

%A _Reinhard Zumkeller_, Oct 01 2003

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 05:38 EDT 2020. Contains 333073 sequences. (Running on oeis4.)