OFFSET
0,3
COMMENTS
For no k do either of the subsequences k(k+1)(k+2)(k+3) or (k+3)(k+2)(k+1)k occur in any permutation.
LINKS
D. M. Jackson and R. C. Read, A note on permutations without runs of given length, Aequationes Math. 17 (1978), no. 2-3, 336-343.
FORMULA
G.f.: Sum_{n>=0} n!*((2*x^m-x^(m+1)-x)/(x^m-1))^n where m = 4. - Ivana Jovovic ( ivana121(AT)EUnet.yu ), Nov 11 2007
PROG
(PARI) seq(n)={my(m=4); Vec(sum(k=0, n, k!*((2*x^m-x^(m+1)-x)/(x^m-1) + O(x*x^n))^k))} \\ Andrew Howroyd, Aug 31 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonas Wallgren, Jun 08 2004
EXTENSIONS
More terms from Ivana Jovovic ( ivana121(AT)EUnet.yu ), Nov 11 2007
a(0)=1 prepended and terms a(20) and beyond from Andrew Howroyd, Aug 31 2018
STATUS
approved