[seqfan] Re: Help with A028247 Number of T-frame polyominoes with n cells

[Don Reble]

> I wonder whether A028247 ought to be extended backward to note that
> there are 0 examples for n=1, 2, and 3.

     Yes: a(1)=0, not "undefined".

> Does a similar sequence to A028247 exist for "L-frame" polyominoes?

     A270060

-- 
Don Reble  djr at nk.ca