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A050521 Number of factorizations of (n,2*n) into pairs (k,l). 1
1, 1, 1, 3, 1, 7, 1, 10, 4, 7, 1, 33, 1, 7, 9, 28, 1, 39, 1, 33, 9, 7, 1, 133, 4, 7, 15, 33, 1, 91, 1, 80, 9, 7, 9, 229, 1, 7, 9, 133, 1, 91, 1, 33, 53, 7, 1, 474, 4, 39, 9, 33, 1, 175, 9, 133, 9, 7, 1, 569, 1, 7, 53, 208, 9, 91, 1, 33, 9, 91, 1 (list; graph; refs; listen; history; text; internal format)
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
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
Cf. A051707.
Sequence in context: A077202 A086665 A273013 * A266724 A247146 A362628
KEYWORD
nonn,nice,easy
AUTHOR
EXTENSIONS
More terms from Sean A. Irvine, Mar 21 2013
STATUS
approved

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Last modified July 23 23:47 EDT 2024. Contains 374575 sequences. (Running on oeis4.)