OFFSET
1,2
COMMENTS
FORMULA
G.f.: x*y*(2-x)/(1-2*x*y)/(1-x)^2. - Vladeta Jovovic, Dec 31 2002
EXAMPLE
Triangle begins 1; 2,0; 3,4,0; 4,6,8,0; 5,8,12,16,0; ...
a(13) = 12 because we find 1 + 3 + 4 + 3 + 1 multisets of type 21^(n-2): they are 4; 14,24,34; 114,124,134,234; 1124,1134,1234; and 11234
CROSSREFS
KEYWORD
AUTHOR
Alford Arnold, Dec 30 2002
EXTENSIONS
More terms from Vladeta Jovovic, Dec 31 2002
STATUS
approved