a(n) and floor[a(n)/2] are both squares; i.e. squares which remain squares when written in base 2 and last digit is removed.
0, 1, 9, 289, 9801, 332929, 11309769, 384199201, 13051463049, 443365544449
1 seqfan posts
Mon Jan 16 10:12:57 CET 2012 [seqfan] Re: Richard Guy's request for several new sequences (amended)