4444444444domain: NAppears in sequencesa(n) = 4*(10^n - 1)/9.at n=10A002278Sum of totient function values of powers of n, as exponent runs from 1 to n.at n=9A091262Repdigit Smith numbers.at n=5A104166a(n)*n = A112897(n).at n=9A112898Repdigit numbers n such that the repeated digit of n is equal to the digital root of n.at n=25A271569