OFFSET
1,4
COMMENTS
Pairs (k,l) must satisfy 0<k, 0<l; if k=1 then l=1. Definition of "*": (a,b)*(x,y)=(a*x,b*y); unit is (1,1).
Factorization is up to ordering of pairs, thus (2,2)*(5,10) is the same as (5,10)*(2,2). Factorizations may involve an arbitrary number of pairs, (2,2)*(3,4)*(5,6)=(30,48). - Sean A. Irvine, Mar 21 2013
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..1000
EXAMPLE
(10,20) = (2,1)*(5,20) = (2,20)*(5*1) = (2,2)*(5,10) = (2,10)*(5,2) = (2,4)*(5,5) = (2,5)*(5,4); so a(10) = 7.
CROSSREFS
KEYWORD
nonn,nice,easy
AUTHOR
EXTENSIONS
More terms from Sean A. Irvine, Mar 21 2013
STATUS
approved