OFFSET
0,6
REFERENCES
D. H. Lehmer, Permutations with strongly restricted displacements. Combinatorial theory and its applications, II (Proc. Colloq., Balatonfured, 1969), pp. 755-770. North-Holland, Amsterdam, 1970.
LINKS
Vladimir Baltic, On the number of certain types of strongly restricted permutations, Applicable Analysis and Discrete Mathematics Vol. 4, No 1 (April, 2010), 119-135
Index entries for linear recurrences with constant coefficients, signature (1, 0, 0, 0, 2, -1, 1, 0, 0, -1).
FORMULA
G.f.: -(x^5-1)/(x^10-x^7+x^6-2*x^5-x+1).
a(n) = a(n-1)+2*a(n-5)-a(n-6)+a(n-7)-a(n-10).
EXAMPLE
G.f. = 1 + x + x^2 + x^3 + x^4 + 2*x^5 + 3*x^6 + 5*x^7 + 7*x^8 + 9*x^9 + ...
a(5) = 2 for permutations [1,2,3,4,5] and [4,5,1,2,3].
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Baltic, Feb 10 2003
STATUS
approved