OFFSET
1,3
COMMENTS
A rooted partition of n is an integer partition of n - 1.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..1000
EXAMPLE
The a(11) = 8 rooted twice-partitions: (9), (333), (111111111), (4)(4), (22)(22), (1111)(1111), (1)(1)(1)(1)(1), ()()()()()()()()()().
MATHEMATICA
Table[If[n===1, 1, DivisorSum[n-1, If[#===1, 1, DivisorSigma[0, #-1]]&]], {n, 100}]
PROG
(PARI) a(n)=if(n==1, 1, sumdiv(n-1, d, if(d==1, 1, numdiv(d-1)))) \\ Andrew Howroyd, Aug 26 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Mar 26 2018
STATUS
approved