The Secundus U(2,F)F
The series around U0:

U-5=F5-5F3+5F
U-4=F4-4F2+2
U-3=F3-3F
U-2=F2-2
U-1=F
U0=2
U1=F
U2=F2-2
U3=F3-3F
U4=F4-4F2+2
U5=F5-5F3+5F
The secundus is symmetric with regard to U0.

It can be derived from the primus by taking the subsequent differences between Un+1 and Un-1 of that series
(with U0 = u1 - u-1 = 2).
Theorems
Theorems have been proved by complete induction.
For every integer k: Un | U(2k-1)n Basic property
Un+1*Un-1 =Un2+(F+2)(F-2) Theorem1
U2n-1 =Un*Un-1 - FTheorem 2.1
U2n =Un2-2Theorem 2.2
Theorem 2 links terms around Un with terms at twice the index value. I call this the series' development 'from the belly'.

The secundus coefficients matrix
The degree of a polynome the same as its index.
Exponents decrease with steps of 2.
Note that each column displays the subsequent differences in the next one, or, to put it another way, each column displays the partial sums of the previous one.
U1:1
U2:1-2
U3:1-3
U4:1-42
U5:1-55
U6:1-69-2
U7:1-714-7
U8:1-820-162
U9:1-927-309
U10:1-1035-5025-2
U11:1-1144-7755-11
U12:1-1254-112105-362
U13:1-1365-156182-9113
U14:1-1477-210294-19649-2
U15:1-1590-275450-378140-15
U16:1-16104-352660-672336-642
U17:1-17119-442935-1122714-20417
U18:1-18135-5461287-17821386-54081-2
U19:1-19152-6651729-27172508-1254285-19
U20:1-20170-8002275-40044290-2640825-1002
U21:1-21189-9522940-57337007-51482079-38521
U22:1-22209-11223740-800811011-94384719-1210121-2
U23:1-23230-13114692-1094816744-164459867-3289506-23
U24:1-24252-15205814-1468824752-2745619305-80081716-1442
U25:1-25275-17507125-1938035700-4420035750-178755005-65025