The Tertius U(1,1)F
The series around U0:

U-5=F5-F4-4F3+3F2+3F-1
U-4=F4-F3-3F2+2F+1
U-3=F3-F2-2F+1
U-2=F2-F-1
U-1=F-1
U0=1
U1=1
U2=F-1
U3=F2-F-1
U4=F3-F2-2F+1
U5=F4-F3-3F2+2F+1
U6=F5-F4-4F3+3F2+3F-1
The tertius is symmetric with regard to U0-U1.
It can be derived from the primus by taking the subsequent differences between Un+1 and Un of that series
(with U0 = u0-u-1 = 1).

Theorems
Theorems have been proved by complete induction.
For every integer k: Un | Un+k(2n-1) Basic property
Un+1*Un-1 =Un2+(F-2) Theorem1
U2n-1+1 =Un(Un+Un-1)Theorem 2.1
U2n+1 =Un(Un+1+Un)Theorem 2.2
U2n-1-1 =(Un+1-Un-1)(Un-Un-1)/(F-2)Theorem 3.1
U2n-1 =(Un+1-Un-1)(Un+1-Un)/(F-2)Theorem 3.2
Theorems 2 and 3 link terms around Un with terms at twice the index value. I call this the series' development 'from the belly'.

The tertius coefficients matrix
Disregarding signs, this matrix is identical to the quartus coefficients matrix.
The degree of a polynome is one less than its index.
Exponents decrease with steps of 1.
Note that the columns come in pairs with an index shift.
U1:1
U2:1-1
U3:1-1-1
U4:1-1-21
U5:1-1-321
U6:1-1-433-1
U7:1-1-546-3-1
U8:1-1-6510-6-41
U9:1-1-7615-10-1041
U10:1-1-8721-15-20105-1
U11:1-1-9828-21-352015-5-1
U12:1-1-10936-28-563535-15-61
U13:1-1-111045-36-845670-35-2161
U14:1-1-121155-45-12084126-70-56217-1
U15:1-1-131266-55-165120210-126-1265628-7-1
U16:1-1-141378-66-220165330-210-25212684-28-81
U17:1-1-151491-78-286220495-330-462252210-84-3681
U18:1-1-1615105-91-364286715-495-792462462-210-120369-1
U19:1-1-1716120-105-4553641001-715-1287792924-462-33012045-9-1
U20:1-1-1817136-120-5604551365-1001-200212871716-924-792330165-45-101
U21:1-1-1918153-136-6805601820-1365-300320023003-1716-1716792495-165-55101
U22:1-1-2019171-153-8166802380-1820-436830035005-3003-343217161287-495-2205511-1
U23:1-1-2120190-171-9698163060-2380-618843688008-5005-643534323003-1287-71522066-11-1
U24:1-1-2221210-190-11409693876-3060-8568618812376-8008-1144064356435-3003-2002715286-66-121
U25:1-1-2322231-210-133011404845-3876-11628856818564-12376-194481144012870-6435-500520021001-286-78121
U26:1-1-2423253-231-154013305985-4845-155041162827132-18564-318241944824310-12870-1144050053003-1001-3647813-1