Euler's partition theorem and the combinatorics of -sequences

Euler's partition theorem and the combinatorics of -sequences Euler's partition theorem and the combinatorics of -sequences

01.06.2015 Views

Let u l and v l be the roots of the polynomial x 2 − lx + 1: Then u l = l + √ l 2 − 4 ; v l = l − √ l 2 − 4 2 2 u l + v l = l; u l v l = 1. a (l) n = un l − v n l u l − v l . For real r, define ∆ (l) r = ul r + v l r . Then for integer n ∆ (l) n = a (l) n+1 − a(l) n−1 . (∆ is the l analog of “2”.) (∆ (l) n/2 )2 = u n l + 2(u lv l ) n/2 + v n l = ∆ (l) n + 2. ∆ (l) −r = u−r l + v −r l = vl r + ur l = ∆(l) r

A 3-term recurrence for the l-nomial [LS] ( n k ) (l) = ( n − 2 k ) (l) + ∆ (l) n−1 ( ) n − 2 (l) + k − 1 ( ) n − 2 (l) k − 2 Proof: Use identities: a (l) n+k − a(l) n−k = ∆(l) n a (l) k . a n (l) a (l) n−1 − a(l) k a(l) k−1 = a(l) n−k a(l) n+k−1 .

Let u l <strong>and</strong> v l be <strong>the</strong> roots <strong>of</strong> <strong>the</strong> polynomial x 2 − lx + 1:<br />

Then<br />

u l = l + √ l 2 − 4<br />

; v l = l − √ l 2 − 4<br />

2<br />

2<br />

u l + v l = l; u l v l = 1.<br />

a (l)<br />

n = un l − v n l<br />

u l − v l<br />

.<br />

For real r, define<br />

∆ (l)<br />

r<br />

= ul r + v l r . Then for integer n<br />

∆ (l)<br />

n<br />

= a (l)<br />

n+1 − a(l) n−1 . (∆ is <strong>the</strong> l analog <strong>of</strong> “2”.)<br />

(∆ (l)<br />

n/2 )2 = u n l + 2(u lv l ) n/2 + v n l = ∆ (l)<br />

n + 2.<br />

∆ (l)<br />

−r = u−r l<br />

+ v −r<br />

l<br />

= vl r + ur l = ∆(l) r

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