OFFSET
1,2
COMMENTS
a(n) is a multiple of n!.
EXAMPLE
a(1) = 1 as '1' is the only sequence of length A373728(1) = 1.
a(2) = 2 corresponding to the sequences of length A373728(2) = 2 : {'12', '21'}.
a(3) = 18 corresponding to the sequences of length A062714(3) = 4 : {'1213', '1231', '1232', '1312', '1321', '1323', '2123', '2131', '2132', '2312', '2313', '2321', '3121', '3123', '3132', '3212', '3213', '3231'}.
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Chai Wah Wu, Jun 27 2024
STATUS
approved