OFFSET
1,2
COMMENTS
Form a sequence of French words as follows: look to the left, towards the beginning of the sequence and write down the number of letters you see; repeat; then replace the words by the corresponding numbers.
The sequence of words is: zero, quatre, dix, treize, dix-neuf, vingt-six, trente-quatre, quarante-six, cinquante-sept, ...
Hyphens, accents and spaces are not counted.
For an English version see A139097.
REFERENCES
E. Angelini, "Jeux de suites", in Dossier Pour La Science, pp. 32-35, Volume 59 (Jeux math'), April/June 2008, Paris.
EXAMPLE
The first word is "zero", because initially there are no letters to the left. The second word is "quatre" (and so a(2)=4), because at the end of the first word we can see four letters to the left. And so on.
PROG
(PARI) A139121(n)={ n>1 & return( #select(Vec(French(n=A139121(n-1))), x->x>"@")+n )} /* see A167507 for French() */ \\ M. F. Hasler, Sep 29 2011
CROSSREFS
KEYWORD
nonn,word
AUTHOR
N. J. A. Sloane (based on Angelini's article), Jun 08 2008, Jun 15 2008
EXTENSIONS
Offset and a(9) corrected (according to wording of example) and terms beyond a(9) from M. F. Hasler, Sep 29 2011
STATUS
approved