OFFSET
0,2
EXAMPLE
a(3) = 4: (2,0),(2,2),(1,1,2,2),(1,1,2,2,3,4)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Frank Ellermann, May 13 2001
EXTENSIONS
a(10) from Naohiro Nomoto, May 10 2002
a(11) and a(12) from Michael Anthony Keyes, May 12 2021
STATUS
approved