The first few numbers in the sequence are: In Douglas Hofstadter's book Metamagical Themas, the sequence is credited to Jeffrey Aronson of Oxford, England.
The proof depends on the observation that the English names of all ordinal numbers, except those that end in 2, must contain at least one "t".
There are many generalizations of Aronson's sequence and research into the topic is ongoing.
However, they criticize it for being ambiguously defined due to the variation in naming of numbers over one hundred in different dialects of English.
In its place, they offer several other self-referential sequences whose definitions rely only on mathematics rather than on the English language.