OFFSET
0,3
COMMENTS
a(n) is also the number of sequences of length 2n on n symbols. - Washington Bomfim, Oct 06 2009
a(n) is the number of endofunctions on [n] that map each even number to an even number and each odd number to an odd number. - Enrique Navarrete, Sep 30 2022
LINKS
Winston de Greef, Table of n, a(n) for n = 0..213 (first 101 terms from Harry J. Smith)
FORMULA
(-1)^n*determinant of the 2n X 2n matrix M_(i, j) = i+j if (i + j) is a multiple of n, M_(i, j) = 1 otherwise. - Benoit Cloitre, Aug 06 2003
a(n) = n! * [x^n] 1/(1 + LambertW(-n*x)). - Ilya Gutkovskiy, Oct 03 2017
Sum_{n>=1} 1/a(n) = A086648. - Amiram Eldar, Nov 16 2020
MATHEMATICA
f[n_]:=n^(2*n); Join[{1}, f[Range[20]]] (* Vladimir Joseph Stephan Orlovsky, Feb 19 2011 *)
PROG
(PARI) a(n) = n^(2*n); \\ Harry J. Smith, Aug 02 2009
(Python)
def A062206(n): return n**(n<<1) # Chai Wah Wu, Nov 18 2022
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jason Earls, Jun 13 2001
EXTENSIONS
Initial term corrected by Reinhard Zumkeller, Jan 30 2009
STATUS
approved