OFFSET
0,12
LINKS
Eric Weisstein's World of Mathematics, Refactorable Number
FORMULA
a(n) = Sum_{j=1..floor(n/3)} Sum_{i=j..floor((n-j)/2)} chi(i/d(i)) * chi(j/d(j)) * chi((n-i-j)/d(n-i-j)), where chi(n) = 1 - ceiling(n) + floor(n) and d is the number of divisors of n (A000005).
EXAMPLE
a(6) = 1; There is one partition of 6 into 3 refactorable parts, (2,2,2).
a(11) = 2; There are two partitions of 11 into 3 refactorable parts, (9,1,1) and (8,2,1).
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, Jun 09 2020
STATUS
approved