OFFSET
1,2
LINKS
P. R. J. Asveld, Generating all permutations by context-free grammars in Chomsky normal form, Theoretical Computer Science 354 (2006) 118-130.
FORMULA
a(n) = Sum_{k=1..n} t(n, k), where t(n, k) is the n-th row of the Pascal-like triangle of A090349.
EXAMPLE
a(4) = 4 + 6 + 0 + 1 = 11; cf. the example grammar of A090349.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Peter R. J. Asveld, Jan 30 2004
STATUS
approved