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Number of n-element nonnegative integer arrays that are ascent sequences (interior element no greater than one plus up-steps preceding it) in both forward and reverse directions
1

%I #5 Mar 31 2012 12:36:48

%S 1,1,2,4,9,23,65,201,679,2489,9831,41673,188858,911216,4664879,

%T 25265271,144350862,867748340,5475788662,36194252078,250093494424,

%U 1803204139718,13543620370665,105800880875545,858375849401380,7222921375625584

%N Number of n-element nonnegative integer arrays that are ascent sequences (interior element no greater than one plus up-steps preceding it) in both forward and reverse directions

%H R. H. Hardin, <a href="/A202552/b202552.txt">Table of n, a(n) for n = 1..116</a>

%e Some solutions for n=7

%e ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0

%e ..0....1....1....0....1....0....0....1....1....1....0....1....0....0....1....1

%e ..1....1....0....1....0....0....0....2....2....0....1....0....1....1....0....1

%e ..2....1....0....0....1....0....1....1....1....0....1....2....0....2....0....1

%e ..1....0....1....1....2....0....0....0....0....1....1....2....0....2....2....1

%e ..1....0....0....1....1....0....1....1....0....1....0....1....0....1....1....1

%e ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0

%K nonn

%O 1,3

%A _R. H. Hardin_ Dec 21 2011