Sorry - pressed send instead of paste! Trying again: ===================================================================== Hello Skip Points:

`0: is this the same Quora which keeps sending me e-messages with headers`

`such as`

"What are the best things for Oxford students to do on weekends?"

`"What is the best and most prestigious English university nowadays?`

`Oxford? Cambridge?"`

- both received yesterday/today!?

`1: A reply has just popped up from a sender which I can only see as`

`"Programming Forum",`

`probably not from Jon Hough, but replying to his comment. It deals in`

`the combinatorial`

`approach which has to be used for larger such problems. It would be nice`

`to know who.`

`2: Here's a smaller brute force approach. Consider valid numbers as`

`sextuplets of digits`

`drawn from 0 1 2, possibly followed by adding 1 to each digit. We`

`don't need to worry at`

all about 3 to 9 to start with. So, (working on digits 0 1 2):

`100 200 300 400 { sext =: 3#.inv i.3^6 NB. show a few members of`

`the set`

0 1 0 2 0 1 0 2 1 1 0 2 1 0 2 0 1 0 1 1 2 2 1 1 +/(3>>./@:((1, 2~:/\])#;.1 ]))"1 sext NB. using cut 492 NB. using first differences of indices of change points +/(3 > >./@(+/\inv) @ (_1,5,~I.@(2~:/\])))"1 sext 492 ts' +/(3 > >./@(+/\inv) @ (_1,5,~I.@(2~:/\])))"1 sext' 0.00453397 8640 ts'+/(3>>./@:((1, 2~:/\])#;.1 ]))"1 sext' 0.00129372 6208 Cheers, Mike On 09/04/2018 06:51, Skip Cave wrote:

Here's a fun math challenge on Quora: Find the number of 6-digit numbers made up of the digits 1, 2, and 3 which have no digit recurring three or more times, consecutively? The link to my answer on Quora is: https://goo.gl/BzBDQe Skip Cave Cave Consulting LLC ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm

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