OFFSET
1,2
FORMULA
a(n) = 2^(n^2)-2*2^((n-1)*n)+2^((n-1)^2).
EXAMPLE
a(2)=10: the monomino, 4 dominoes (2 strictly disconnected), 4 rotations of the L tromino, and the square tetromino.
PROG
(PARI) a(n) = 2^(n^2) - 2*2^((n-1)*n) + 2^((n-1)^2); \\ Michel Marcus, Aug 30 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
David Bevan, Jul 27 2009
STATUS
approved