sashamakarenko/collatz

3n+1 differently

3n+1 problem proof and computer programs

Proof

For details read makarenko-alexandre-3n+1.pdf

New/different formulation

Change 1 - Instead of dividing even numbers by 2 we add 1 shifted left by the number of trailing zeros T.

Change 2 - The sequence ends when it reaches . In other words, eventually there will be only single 1 shifted left by the number of divisions by 2 we would accomplish with the regular Collatz algorithm.

Example for 11:

step	old decimal	old binary	new binary	new decimal
0	11	1011	1011	11
	*3	100001	100001	*3
	+1	100010	100010	+1
	/2	10001	100010	nop
1	17	10001	100010	34
	*3	110011	1100110	*3
	+1	110100	1101000	+2
	/4	1101	1101000	nop
2	13	1101	1101000	104
	*3	100111	100111000	*3
	+1	101000	101000000	+8
	/8	101	101000000	nop
3	5	101	101000000	320
	*3	1111	1111000000	*3
	+1	10000	10000000000	+64
	/16	1	10000000000	nop
4	1	1	10000000000	1024

Each new sequence value will be :

where is the number of trailing zeros in the value .

Reverse algorithm

Given a value we can find all possible with

by evaluating all .

Example of all values reverted from

step 0	step 1	step 2	step 3	step 4	step 5	binary
1024						10000000000
	341					101010101
	340					101010100
		113				1110001
	336					101010000
	320					101000000
		106				1101010
			35			100011
		104				1101000
			34			100010
				11		1011
		96				1100000
	256					100000000
		85				1010101
		84				1010100
		80				1010000
			26			11010
			24			11000
		64				1000000
			21			10101
			20			10100
				6		110
			16			10000
				5		101
				4		100
					1	1

The backward algorithm is combinatorial where the values reverted from and never overlap.

Proof. By tending and to infinity the backward sequence will produce all integers.

Code

In src all java files are standalone programs. To compile for example ForwardCollatz.java:

$> javac ForwardCollatz.java

Forward sequence

Example: solve Collatz in new formulation for 47:

Backward sequence

Example: solve reverse Collatz for 47 starting from 2^68:

Benchmarks

See in bench directory.