OFFSET
2,2
LINKS
Antonio Bernini, Luca Ferrari, and Einar SteingrÃmsson, The Möbius function of the consecutive pattern poset, Electron. J. Combin., 18(1):Paper 146, 12 pp., 2011.
Sergi Elizalde, Peter R. W. McNamara, The structure of the consecutive pattern poset, arXiv:1508.05963 [math.CO], 2015.
Bruce E. Sagan and Robert Willenbring, Discrete Morse theory and the consecutive pattern poset, J. Algebraic Combin., 36(4):501-514, 2012.
EXAMPLE
For n=3, we have a(3)=4 because the permutations 132, 213, 231, 312 have exterior equal to 1, and thus contained in their interior. On the other hand, 123 has exterior 12, and 321 has exterior 21.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Sergi Elizalde, Oct 28 2015
STATUS
approved