A224919 Start with a(1),...,a(5) = 6,20,4,4,45 and successively append f(a(3)), f(a(4)), f(a(5)), ... to the sequence, where f maps 4 to 9, 9 to 45 and 45 to 4,4,4,4,4,4,4,4,4,45.

6, 20, 4, 4, 45, 9, 9, 4, 4, 4, 4, 4, 4, 4, 4, 4, 45, 45, 45, 9, 9, 9, 9, 9, 9, 9, 9, 9, 4, 4, 4, 4, 4, 4, 4, 4, 4, 45, 4, 4, 4, 4, 4, 4, 4, 4, 4, 45, 4, 4, 4, 4, 4, 4, 4, 4, 4, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 9, 9, 9, 9, 9, 9, 9, 9, 9, 4, 4, 4, 4, 4, 4, 4, 4, 4, 45, 9, 9, 9, 9, 9, 9, 9, 9, 9, 4, 4, 4, 4, 4, 4, 4, 4, 4, 45

Offset

1,1

Comments

This infinite sequence has the curious property that if the entries are written in English and a thin vertical line is inserted after every e, the numbers of letters between the vertical lines is the same as the sequence. Spaces, commas and hyphens are to be ignored.

References

Eric Angelini, Postings to Math Fun Mailing List, Dec 13 2011 - Dec 15 2011.

Links

Table of n, a(n) for n=1..105.

Example

The first four stages in the growth of the sequence are:
6 20 4 4 45
9 9 4 4 4 4 4 4 4 4 4 45
45 45 9 9 9 9 9 9 9 9 9 4 4 4 4 4 4 4 4 4 45
4 4 4 4 4 4 4 4 4 45 4 4 4 4 4 4 4 4 4 45 45 45 45 45 45 45 45 45 45 9 9 9 9 9 9 9 9 9 4 4 4 4 4 4 4 4 4 45
...
The sequence with the vertical lines inserted:
six twe|nty four four forty-five| nine| nine| four four four four four four four four four forty-five| forty-five| forty-five| nine| nine| nine| nine| nine| nine| nine| nine| nine| four four four four four four four four four forty-five| four four four four four four four four four forty-five| four ...

Crossrefs

Sequence in context: A060748 A176559 A241715 * A282377 A281936 A075251

Adjacent sequences: A224916 A224917 A224918 * A224920 A224921 A224922

Keyword

nonn,word,base

Author

N. J. A. Sloane, Apr 19 2013

Status

approved