I found a sequence that many participants in this forum must have brushed into in the past. I think I'm not the only one here who calculated the first dozen or twenty entries in this sequence back in the 1970s. And yet it's not on OEIS ... and I'm not sure it should be. I don't want to give the definition in this message ... I want to see how many other math-funsters recognize it. It's zero-origin, and a[5] is the place OEIS gives up. Here are the values of a[0] through a[20]; let's have the first few replies to this message merely affirm that they recognize the sequence, or express bafflement, and we can give the answer a little later. 0 1 1 0 2 6 12 14 48 20 2 15 15 24 28 40 32 24 20 25 20 After we do the reveal, I'd like to know how much is known about the asymptotic behavior of the sequence.