20202020

Appears in sequences

• Łukasiewicz words for the rooted plane binary trees (interpretation d in Stanley's exercise 19) with the last leaf implicit, i.e., these words are given without the last trailing zero, except for the null tree which is encoded as 0.at n=9A071152
• Quadruplets: base 10 representation is the juxtaposition of four identical strings.at n=19A074843