OEIS A244953: Ridiculous Formula

[C.Ret]

(08-20-2022 11:34 AM)Thomas Klemm Wrote:  How about:\( \begin{align} a(n) = \frac{3n + 4 - (n \mod 4 - 2)^2}{2} \end{align} \)

Very nice formula that will be efficient for large \( n \), but actually lead to a longer program than the simple original definition : \( a(n)=\begin{align}\sum_{k=0}^{n}mod(-k,4)\end{align} \)

A001 LBL A
A002 INPUT N
A003 0
A004 RCL ST Y  CHS  4  Rmdr  +  DSE ST Y  GTO A004
A011 RTN

Of course, this shorter version of the code need more time to compute a(n) for large n.

PS: Step A002 is optional, it is just the equivalent of a "N=?" PROMPT operation. Just to remember the user to enter a real integer.