5987822380domain: NAppears in sequencesExpansion of c(3*x^2)/(1-x*c(3*x^2)), c(x) the g.f. of A000108.at n=21A128386Number of quaternary words either empty or beginning with the first character of the alphabet, that can be built by inserting n doublets into the initially empty word.at n=11A194724