Quadratic Derivations and Uniform Modular Periods for Six Inverse-Function Sequences

We study the integral derivation D(s)=cᵃ, D(c)=scᵃ⁻¹ on the quadratic algebra Z[s,c]/(c²-s²-1), with even-derivative columns of inverse-function flows as integer-sequence observables. We prove a uniform eventual-period theorem modulo every positive integer for all even exponents, including a separate vanishing-prime analysis. The same framework gives full-index consequences for five OEIS inverse-function sequences. For the odd exponent $a=5$ we establish prime-power eventual vanishing away from $2$ and $3$, a two-adic period lifting and a three-adic period lifting, settling both precise source conjectures for A281428. The arguments use integral differential operators, finite free rings, restricted characteristic-p derivations, and the Chinese remainder theorem. We distinguish the original source definitions and recurrences from the congruence theorems established here. Licensing note: The manuscript is licensed under CC BY 4.0. The OEIS b-file snapshots included in the supplementary archive retain their original CC BY-SA 4.0 license and attribution. The independently authored verification code is made available under CC BY 4.0.