%I
%S 2,5,10,16,26,42,68,110,178,288,466,754,1220,1974,3194
%N Number of distinct permutations generated by shuffling n cards with "clump size" <= 2.
%C Take a deck of n cards, cut into two nonempty piles, then do a riffleshuffle in which no more than 2 consecutive cards fall from the same half. Sequence gives number of distinct npermutations that result.
%F For n>3, a(n) = 2 * F(n+1), with F(n) = A000045(n).
%e a(4)=10 because we can split the deck as 1234 then shuffle to get 2134 or 2314, or split as 1234 and get 3421 1324 1342 3124 3142 or split 1234 and get 1243, 1423. These plus the identity (1234) give 10 permutations in all.
%Y Essentially the same as A006355.
%K nonn
%O 2,1
%A Mike Keith (domnei(AT)aol.com)
