OFFSET
1,2
EXAMPLE
For n = 2 there are 4 such sequences: (1,1), (1,2), (2,1), and (2,2).
The corresponding lengths of longest (not necessarily strictly) increasing subsequences of these is 2, 2, 1, 2, so a(2) =7.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jeffrey Shallit, Aug 02 2016
EXTENSIONS
a(8)-a(13) from Alois P. Heinz, Nov 02 2018
STATUS
approved