## A small child has a “number caterpillar” consisting of forty jigsaw pieces, each with one number on it, which, when connected together in a line, reveal the numbers $1$ to $40$ in order.

Every night, the child’s father has to pick up the pieces of the caterpillar that have been scattered across the play room. He picks up the pieces at random and places them in the correct order. As the caterpillar is built up in this way, it forms distinct segments that gradually merge together. The number of segments starts at zero (no pieces placed), generally increases up to about eleven or twelve, then tends to drop again before finishing at a single segment (all pieces placed).

For example:

Piece Placed

Segments So Far

121422936434554354……

Let $M$ be the maximum number of segments encountered during a random tidy-up of the caterpillar.

For a caterpillar of ten pieces, the number of possibilities for each $M$ is

M

Possibilities

1512 2250912 31815264 41418112 5144000

so the most likely value of $M$ is $3$ and the average value is $385643/113400 = 3.400732$, rounded to six decimal places.

The most likely value of $M$ for a forty-piece caterpillar is $11$; but what is the average value of $M$?

Give your answer rounded to six decimal places.

### The problem requires calculating the average maximum number of segments in a caterpillar puzzle of 40 pieces.

This problem involves the concepts of permutations and dynamic programming. To solve it, we need to see how a new piece can extend an existing segment or create a new one.

For that purpose, we create an array dp[i][j][k], where i is the number of pieces already placed, j is the number of segments so far, and k is the maximum number of segments so far. Initializing dp array with 0s at the beginning is our first step.

Let’s exemplify: dp[i][j][k] can result from placing the next piece to extend a segment or to create a new segment.

1. When we add the next piece to an existing segment, the piece could extend any one of the j segments, and the total number of segments will still be j. The maximum number of segments so far remains k.

2. When we create a new segment, the number of segments increases by 1 and the total number of segments becomes j + 1. The maximum number of segments so far could be the maximum of the previous maximum number of segments and j+1. So, we have to evaluate two cases.

Now, iterating through the number of pieces and the number of segments, we add up the results in the dp array according to the previous explanation.

After this process, we can compute the desired average by using a weighted sum formula. For this, we sum up the product of each maximum number of segments and the product of its likeliness and that maximum number.

This results in:

`numerator = SUM(i*dp[40][j][i] for every i and j)`

`denominator = SUM(dp[40][j][i] for every i and j)`

The average is then calculated as `average = numerator / denominator`.

Since the calculations involved in this problem are computationally intensive, a desire to implement and run the algorithm in an efficient programming language would yield the precise numerical value up to six decimal places.

Please note, since it requires substantial programming effort and computational resources, it might be outside the realm of a human tutor’s capabilities to provide the precise numeric answer.

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$250250$Cardano Triplets

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