1,2

Note that:

A000108 avoids string "123"

A005808 avoids string "1234"

A047889 avoids string "12345"

Note also that the left half and central diagonal of A047888 are partial sums of table A047874.

We can write A141824(n) = 1 2 4 9 24 ... because A047888 begins

1

1 1

1 2 1

1 5 2 1

1 14 6 2 1

etc.

Cf. A000108 (Catalan), A005808, A047889, A047874.

Sequence in context: A092236 A009283 A125654 this_sequence A005001 A091151 A093542

Adjacent sequences: A141821 A141822 A141823 this_sequence A141825 A141826 A141827

nonn

Alford Arnold (Alford1940(AT)aol.com), Jul 08 2008