OFFSET
0,1
COMMENTS
Based on the observation by Diane Karloff that the trajectory of A005589 always converges to 4.
40311123323 (concatenation of the first seven terms) is the first time prime is obtained when concatenating k first initial terms of the sequence. - Jonathan Vos Post, Jul 06 2013, edited by Antti Karttunen, Jul 25 2013
EXAMPLE
"eleven" has 6 letters, "six" has 3 letters, "three" has 5 letters, "five" has 4 letters.
So a(4)=11, as A005589^4(11)=4 and 11 is the first such number.
But a(3)=1, because "one" is the same length as "six".
CROSSREFS
KEYWORD
nonn,word
AUTHOR
Roland Kneer, Jul 05 2013
STATUS
approved