

A084080


Length of lists created by n substitutions k > Range[k+1,1,3] starting with {1}, counting down from k+1 to 1 step 3.


1



1, 1, 1, 2, 3, 4, 9, 15, 22, 52, 91, 140, 340, 612, 969, 2394, 4389, 7084, 17710, 32890, 53820, 135720, 254475, 420732, 1068012, 2017356, 3362260, 8579560, 16301164, 27343888, 70068713
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OFFSET

0,4


COMMENTS

Would appear to coincide with row sums of the inverse of the Riordan array (1x^3,x(1x^3)). These row sums have g.f. 1/(1yy^3+y^4) where y^4y+x=0.  Paul Barry, May 10 2005


LINKS

Table of n, a(n) for n=0..30.


EXAMPLE

{1}, {2}, {3}, {4, 1}, {5, 2, 2}, {6, 3, 3, 3}, {7, 4, 1, 4, 1, 4, 1, 4, 1}


MATHEMATICA

Length/@Flatten/@NestList[ # /. k_Integer:>Range[k+1, 1, 3]&, {1}, 21]


CROSSREFS

Cf. A124753.
Sequence in context: A288856 A033076 A121431 * A124753 A248647 A284437
Adjacent sequences: A084077 A084078 A084079 * A084081 A084082 A084083


KEYWORD

nonn


AUTHOR

Wouter Meeussen, May 11 2003


STATUS

approved



