Question 1089737

Hi I would like know how to get the formula for this sequence 5;6;8;11;15 
<pre>Contrary to someone saying that a formula doesn't exist, one DOES, just in case you want to find the 100th, 2,000th, or 19th term.
That formula is: {{{highlight_green(matrix(1,7, a[n], "=", (1/2)n^2 - (1/2)n + 5, or, a[n], "=", n^2/2 - n/2 + 5))}}}
He has ABSOLUTELY no idea what he's talking about. Quite a few of them are on this site: CLUELESS!!