100000000009domain: NAppears in sequencesSmallest k such that the concatenation 123...(k-1) k (k-1)...321 ( a concatenation of natural numbers from 1 to k and back to 1) is a multiple of prime(n), or 0 if no such number exists.at n=26A07718710*n^n+(n-1).at n=9A089211a(n) = n + (n+1)^(n+2).at n=9A155499a(n) = 10^n + 9.at n=11A253213