

A210540


Number of arrays of n nonnegative integers with value i>0 appearing only after i1 has appeared at least 3 times.


9



1, 1, 1, 1, 2, 4, 8, 17, 40, 104, 291, 857, 2634, 8455, 28424, 100117, 368465, 1410903, 5599073, 22968514, 97267342, 424927846, 1913764155, 8877181958, 42358589064, 207639979365, 1044360973987, 5384167878948, 28429186870051, 153638182314504, 849295001319211
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OFFSET

0,5


LINKS



FORMULA

a(n) = 1 if n<=3 else Sum_{i=0..n3} binomial(n3,i)*a(i). Proved by R. J. Mathar in the Sequence Fans Mailing List.


EXAMPLE

Some solutions for n=11
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..1....1....0....1....1....1....0....1....1....1....1....1....1....1....1....0
..0....1....1....0....1....1....1....0....1....0....0....0....1....1....0....0
..1....1....0....1....0....1....1....0....1....1....0....1....1....1....1....1
..1....0....1....1....1....0....1....0....2....1....0....1....2....2....0....0
..2....2....0....2....2....2....0....0....0....1....1....0....1....2....0....0
..2....0....0....2....2....2....0....1....1....0....1....1....2....2....0....1
..2....1....0....1....0....1....2....0....1....0....2....0....2....2....1....1
..3....1....1....0....2....2....0....1....0....2....1....0....2....0....2....1


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



