OFFSET
0,3
COMMENTS
As usual, "mod 3" means to choose the unique representative in { 0,1,2 } of the equivalence class modulo 3Z.
Here the conventions of A014138 are used, but it seems somehow unnatural to start with offset 0 corresponding to the Catalan number A000108(1).
For m>1, the length of the m-th block of nonzero elements (and thus the approximate length of the m-th string of consecutive 1's) is given by 2 A137822(m)-1.
FORMULA
PROG
(PARI) A137993(n) = lift( sum( k=1, n+1, binomial( 2*k, k )/(k+1), Mod(0, 3) ))
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
M. F. Hasler, Mar 16 2008
STATUS
approved