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Explorations of the Collatz Conjecture - Moravian College

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Therefore, v and v ′ are block or string prefixes if and only if:<br />

∣ ∑k−1<br />

1 =<br />

1 ( 3<br />

(v ′<br />

∣ 2 k−i k +v′ k−1 +...+v′ i+2 ) v ′ i+1 − ) 3(v k+v k−1 +...+v i+2 ) 3 (v′ k +t k−1+...+v ∣∣∣∣∣∣ ′<br />

2 +v′ 1 )<br />

v i+1 + .<br />

2 k<br />

i=0<br />

□<br />

4.2.3 Switching 0’s and 1’s<br />

Since we discovered earlier that corresponding blocks and strings are just permutations<br />

<strong>of</strong> each o<strong>the</strong>r, we began to look at what would happen if we took a parity<br />

sequence and moved <strong>the</strong> ones around to form a new permutation <strong>of</strong> <strong>the</strong> original.<br />

If we take a single 1 and have it switch positions with an adjacent 0, we have <strong>the</strong><br />

following result.<br />

Lemma 5. Given a parity sequence v = 〈v 1 , v 2 , ..., v k−1 , v k 〉 such that v a = 1 and<br />

v a+1 = 0 for some a < k, if we form a new parity sequence v ′ by switching v a and<br />

v a+1 , <strong>the</strong>n T v ′(x) − T v (x) = ∆ where<br />

∆ = 3v a+2+v a+3 +...+v k<br />

2 k−a+1 .<br />

Pro<strong>of</strong>. Given v as stated above, we will use<br />

v ′ = 〈v 1 , v 2 , ...v a−1 , v a+1 , v a , v a+2 , ..., v k−1 , v k 〉<br />

and we will let n be <strong>the</strong> number <strong>of</strong> ones in v and v ′ . From Equation 3.1 and<br />

Theorem 6 we know that when v is applied to a number x<br />

∑<br />

T v (x) = 3n<br />

k−1<br />

2 x + k<br />

i=0<br />

31<br />

3 (v k+v k−1 +...+v i+2 )<br />

2 k−i v i+1 .

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