(D3)How many subsets of (a,b,c, … x,y,z) contain no letters neighboring each other in the English ABC (26 letters)?

(D4)How many "words" (i.e, ordered subsets from (a,b,c, … x,y,z)) contain no neighboring letters that neighbor each other in the English ABC (26 letters)?

(In reply to re: solution to part 1; thoughts on part 2 by Ady TZIDON)

According to Wikipedia the current Hawaiian language has 13 letters. Per the OEIS sequence I cite, that has over 800 million ways just of valid "words" that contain all the letters. There's probably be one or two billion altogether, and the way my program works is to find each one and count them. I think my computer's automatic logoff would take place before a solution was found.

Posted by Charlie on 2014-03-26 08:55:42