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EXAMPLE
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a(1)=5*10^0=5: a(2)=5*10=50; a(3)=5*10^2=500 [From Vincenzo Librandi, Aug 02 2010]
From Adi Dani, May 17 2011: (Start)
a(2)=50: there are 50 compositions of even natural numbers into 2 parts <=9:
(0,0);
(0,2),(2,0),(1,1);
(0,4),(4,0),(1,3),(3,1),(2,2);
(0,6),(6,0),(1,5),(5,1),(2,4),(4,2),(3,3);
(0,8),(8,0),(1,7),(7,1),(2,6),(6,2),(3,5),(5,3),(4,4);
(1,9),(9,1),(2,8),(8,2),(3,7),(7,3),(4,6),(6,4),(5,5);
(3,9),(9,3),(4,8),(8,4),(5,7),(7,5),(6,6);
(5,9),(9,5),(6,8),(8,6),(7,7);
(7,9),(9,7),(8,8);
(9,9). (End)
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