cp's OEIS Frontend

A139212 Number of vowels in the preceding terms spelled out in French.

%I A139212 #11 Jun 14 2017 01:04:09
%S A139212 0,2,4,7,8,10,11,13,16,19,22,25,27,29,32,36,39,43,49,55,60,64,71,78,
%T A139212 85,90,95,102,105,107,109,112,116,120,122,126,129,133,138,143,150,155,
%U A139212 161,168,175,183,190,196,204,210,214,221,227,232,239,246,254,264,274,285,293,303,308,313,319,325,330,335,341,350,357,365,373,383
%N A139212 Number of vowels in the preceding terms spelled out in French.
%C A139212 Form a sequence of French words as follows: look to the left, towards the beginning of the sequence and write down the number of vowels you see; repeat; then replace the words by the corresponding numbers.
%C A139212 The sequence of words is: zero, deux, quatre, sept, huit, dix, onze, treize, seize, ...
%C A139212 Hyphens, accents and spaces are not counted.
%D A139212 E. Angelini, "Jeux de suites", in Dossier Pour La Science, pp. 32-35, Volume 59 (Jeux math'), April/June 2008, Paris.
%e A139212 The second word is "deux" (and so a(2)=2 for the 'e' and the 'u'), because at the end of the first word ("zéro") we can see two vowels ('e' and 'o') to the left.
%o A139212 (PARI) a(n)={ n>1 || return;#select(Vec(French(n=a(n-1))),x->setsearch(Vec("aeiou"),x))+n }  /* see A167507 for French() */
%o A139212 /* Version with memoization for better performance when n >> 100: */
%o A139212 A139212(n)={ type(a139212)!="t_VEC" && a139212=[];
%o A139212 n > #a139212 && a139212=concat( a139212,vector(n-#a139212));
%o A139212 (a139212[n] || n==1) && return(a139212[n]);
%o A139212 a139212[n]=/*up to here only memoization, could be omitted*/
%o A139212 #select(Vec(French(A139212(n-1))), x->setsearch(Vec("aeiou"),x))) + A139212(n-1) } \\ _M. F. Hasler_, Sep 29 2011
%Y A139212 For an English version see A139282.
%K A139212 nonn,word,easy
%O A139212 1,2
%A A139212 _N. J. A. Sloane_ (based on Angelini's article), Jun 08 2008
%E A139212 Fixed offset (according to example) and typo in example. M. F. Hasler, Sep 29 2011