00:01
Okay, we're given this recurrence relation for a sequence of a's.
00:07
And one thing we can note is a of n plus two depends on a sub n.
00:13
It doesn't depend on a of n plus one.
00:17
So in particular, the even and odd values are separate.
00:26
So it really creates two sequences, a sequence of n equals odd values and a sequence of n equals even values.
00:35
And because a of one is zero, that means that for the odd ones, so a of two k plus one equals zero for all k.
00:47
And so any integer k you pick up, the odd terms are gonna be zero.
01:00
For the even terms, let's write out the first few.
01:22
So what's going on here? well, first of all, it switches sign every time.
01:30
So it keeps flipping the sign back and forth.
01:32
And then the denominator is gonna take whatever the last one was and multiply by the next two integers.
01:43
And in fact, if i look at these denominators, i can maybe recognize them.
01:48
The first one is two factorial...