login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual appeal: Please make a donation to keep the OEIS running! Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A122180 Number of ways to write n as n = x*y*z with 1 < x < y < z < n. 7
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 3, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 3, 0, 0, 0, 0, 0, 1, 0, 2, 0, 0, 0, 3, 0, 0, 0, 1, 0, 3, 0, 0, 0, 0, 0, 4, 0, 0, 0, 1, 0, 1, 0, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,48

COMMENTS

x,y,z are distinct proper factors of n. See A122181 for n such that a(n) > 0.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..1001

Index entries for sequences computed from exponents in factorization of n

FORMULA

a(n) = A200214(n)/6. - Antti Karttunen, Jul 08 2017

EXAMPLE

a(48) = 2 because 48 = 2*3*8 = 2*4*6, two products of three distinct proper factors of 48.

PROG

(PARI) for(n=1, 105, t=0; for(x=2, n-1, for(y=x+1, n-1, for(z=y+1, n-1, if(x*y*z==n, t++)))); print1(t, ", "))

(PARI) A122180(n) = { my(s=0); fordiv(n, x, if((x>1)&&(x<n), for(y=x+1, n-1, for(z=y+1, n-1, if(x*y*z==n, s++))))); (s); }; \\ Just slightly optimized from the above. - Antti Karttunen, Jul 08 2017

CROSSREFS

Cf. A034836, A088432, A088433, A088434, A122179, A122181, A200214.

Sequence in context: A101638 A070141 A088722 * A033772 A086015 A249856

Adjacent sequences:  A122177 A122178 A122179 * A122181 A122182 A122183

KEYWORD

nonn

AUTHOR

Rick L. Shepherd, Aug 23 2006

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy .

Last modified November 18 10:38 EST 2017. Contains 294887 sequences.