Let a(k) denote the k-digit repdigit formed by repeating the digit a, and let a∈{1,2,3,4,5,6,7,8,9}. A repdigit is a Niven number when
10k≡1(mod9ka).
Define
m0=37,m1=333667,m21=757,m22=440334654777631,
m31=163,m32=9937,m33=2462401,m34=676421558270641,
m35=130654897808007778425046117.
Repdigit Niven-number parametrization conjecture. The solutions of the repdigit Niven-number equation are parameterized by
k=k{nαβγδ}=3n⋅m0α⋅m1β⋅m21γ1⋅m22γ2⋅m31δ1⋅m32δ2⋅m33δ3⋅m34δ4⋅m35δ5,
where
{α,β,γ1,γ2,δ1,δ2,…,δ5}∈N0
and the minimal-index constraints are
n≥0if all exponents are zero,
n≥1if α=0,n≥2if β=0,
n≥3if {γ1,γ2}={0},n≥4if {δ1,…,δ5}={0}.
The parametrization is intended to demonstrate infinitely many repdigit Niven numbers, which are consequently permutation-invariant Niven numbers; the source does not provide evidence resolving whether this proposed parametrization is complete.