1,2

a(5) = 114 because all but the 6 permutations 23451, 24351, 32451, 34251, 42351, 43251 on 5 letters become 12345 after at most 3 passes through the stack sorter.

Cf. A000139.

Adjacent sequences: A134661 A134662 A134663 this_sequence A134665 A134666 A134667

Sequence in context: A152325 A152329 A054872 this_sequence A068199 A128088 A069657

hard,nonn

Eric S Rowland (erowland(AT)math.rutgers.edu), Jan 25 2008