Tool to generate Conway sequences. The Conway Sequence is a sequence of digits (also called Look-and-Say sequence) invented by mathematician John H. Conway. Each term is made of the reading of the digits (the number of consecutive digits) of the previous term.

Conway Sequence - dCode

Tag(s) : Mathematics, Fun

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Tool to generate Conway sequences. The Conway Sequence is a sequence of digits (also called Look-and-Say sequence) invented by mathematician John H. Conway. Each term is made of the reading of the digits (the number of consecutive digits) of the previous term.

To generate the next term in the sequence, it must use the previous one, read it digit by digit and locate the numbers that are repeated consecutively. The sequence usually begins with 1 first term (also called seed).

Example:

Term | Is read | Is written |
---|---|---|

1 | one 1 | 11 |

11 | two 1s | 21 |

21 | one 2 and one 1 | 1211 |

1211 | one 1, one 2 and two 1s | 111221 |

111221 | three 1s, two 2s and 1 | 312211 |

Example: The Conway sequence is 1, 11, 21, 1211, 111221, 312211, 13112221, 1113213211, ...

The sequence with seed 1 contains only the digits 1, 2 and 3.

All terms begin with 1 or 3 except the 3rd.

Reductio ad absurdum :

Suppose that 333 appears for the first time at term n, then the term n-1 must also contain 333 (_333 or 333_ can only appear with a series of three 3 in the previous term). Contradiction, the hypothesis is false, so 333 never appears.

The Conway sequence is set to begin with 1 by default, but it is possible to consider a different seed.

For a seed g of 2,3,4,5,6,7,8,9 or 0, these values are obtained:

Example: g, 1g, 111g, 311g, 13211g, 111312211g ... (the seed is always at the end).

It is possible to use slightly different rules:

- Read the previous term and count all occurrences of numbers, listed in ascending order.

Example: 1, 11, 21, 1112, 3112, 211213, 312213, 212223, 114213, 31121314, 41122314, ...

- Read the previous term and count all occurrences of numbers, listed in descending order.

Example: 1, 11, 21, 1211, 1231, 131221, 132231, 232221, 134211, 14131231, 14231241, ...

- Read the previous term and count all occurrences of numbers, listed in order of appearance.

Example: 1, 11, 21, 1211, 3112, 132112, 311322, 232122, 421311, 14123113 ...

The Conway sequence is similar to run-length encoding.

`// Yves PRATTER`

// Version 1.0 - 2011/11/07

function previousConway(t) {

r = "";

// impossible

if (t.length%2 == 1) return r;

idx = 0;

while (idx < t.length){

for(i=0; i < t.charAt(idx); i++) { r += t.charAt(idx+1); }

idx += 2;

}

return r;

}

function conway(t) {

if (t == "") return "0";

r = "";

idx = 0;

while (idx < t.length){

for(i=1; t.charAt(idx+i) == t.charAt(idx); i++) {}

r += i + t.charAt(idx);

idx += i;

}

return r;

}

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