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PROJECT EULER · #0872

Recursive Tree

Statement only · SolvedOriginal problem ↗

A sequence of rooted trees Tn is constructed such that Tn has n nodes numbered 1 to n.

The sequence starts at T1, a tree with a single node as a root with the number 1.

For n>1, Tn is constructed from Tn1 using the following procedure:

  1. Trace a path from the root of Tn1 to a leaf by following the largest-numbered child at each node.
  2. Remove all edges along the traced path, disconnecting all nodes along it from their parents.
  3. Connect all orphaned nodes directly to a new node numbered n, which becomes the root of Tn.

For example, the following figure shows T6 and T7. The path traced through T6 during the construction of T7 is coloured red.

0872_tree.png

Let f(n,k) be the sum of the node numbers along the path connecting the root of Tn to the node k, including the root and the node k. For example, f(6,1)=6+5+1=12 and f(10,3)=29.

Find f(1017,917).

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