1,4

Noonan and Zeilberger conjecture that a(n) = (59*n^2+117*n+100)/2/n/(2*n-1)/(n+5)*binomial(2*n,n-4).

J. Noonan and D. Zeilberger, [math/9808080] The Enumeration of Permutations With a Prescribed Number of ``Forbidden'' Patterns

T. Mansour and A. Vainshtein, Counting occurrences of 123 in a permutation.

Cf. A003517, A084249.

Sequence in context: A127520 A009134 A009137 this_sequence A069515 A056350 A056344

Adjacent sequences: A001086 A001087 A001088 this_sequence A001090 A001091 A001092

nonn

John Thomas Noonan [ noonan(AT)euclid.math.temple.edu ]