# a property of multisets: unit fractions with a twist

hv at crypt.org hv at crypt.org
Tue Dec 18 23:22:59 CET 2007

```Hello Seqfans,

It's my first post here so let me introduce myself:
English is not my language and I'm not mathematician, my origin are Computer Sciences.
I apologise in advance for rude errors I'll made, sooner or later ;)

Sequence definition:
Different binary patterns in the set of all permutations Sn taken modulo 2.
Example: 0,1,2,3,4 modulo 2 = 0,1,0,1,0
Short calculation gives sequence:
;N             0  1  2  3  4   5   6   7   8    9
;                  1, 2, 3, 6, 10, 20, 35, 70, 126
;A001405: 1, 1, 2, 3, 6, 10, 20, 35, 70, 126, 252, 462, 924, 1716

Recently, I thought that such binary patterns are of use in  the problem I'm researching.
That assumption turned to be wrong so I had no reason to go any deeper into that sequence.
However, I'm fairly confident that the sequence in question is A001405 indeed.

What is your opinion, is it realy A001405?

Reason why I'm posting this is:
1. I see no explicite corellation with permutations there, or I've overlooked something.
2. Sequence definition over Sn seems simplest than definition(s) given in OEIS,
from my point of view at least.

Is it worth of noting it there?
If so, can you assist me to do that.
I do not pretend that my english and math terminology is good enough.

Best regards,
--ivica
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