# [seqfan] Re: A173279 and A173280

Richard Mathar mathar at strw.leidenuniv.nl
Mon Feb 22 21:12:18 CET 2010

```http://list.seqfan.eu/pipermail/seqfan/2010-February/003727.html finds

kb> From seqfan-bounces at list.seqfan.eu Mon Feb 22 20:36:40 2010
kb> Date: Mon, 22 Feb 2010 20:09:43 +0100
kb> From: Klaus Brockhaus <klaus-brockhaus at t-online.de>
kb> To: Sequence Fanatics Discussion list <seqfan at list.seqfan.eu>
kb>
kb> Does that suffice? What about
kb>
kb> %N A173317 a(n)=5*n!-1
kb> %F A173317 a(n)=5*n!-1

In this case, repeating what's already known is superfluous. However,
using a formula line to repeat the definition to hammer down the meaning
of what's found in the %N line makes perfect sense. If strange acronyms
like "usigma", "sopf" "guuglehupf" and the more standard "sigma", "tau"
"factorial" words are used in the definition, I'd prefer to see them
again as  a(n) = Axxx(...Ayyy(n)) repeated in the formula line to be convinced
that the definition is sound proof. Here, for example "a(n)="
in the definition is superfluous, because "a(n) is" is some sort of
default in the definition. The formula could, of course, not stand without a(n).

Here, this sort of repetition makes sense to verify that the exclamation
mark in the definition is not an emphatic n but a factorial:

%N A173317 5*n!-1.
%F A173317 a(n) = 5*A000142(n)-1.

```