Sum_{i=1..(10^n - 1)/9} i, or ((10^n -1)/9)*((10^n -1)/9 +1)/2 (n-th term is the middle 2(n-1) digits of the (n+9)-th term for n > 1).
A003555
Sum_{i=1..(10^n - 1)/9} i, or ((10^n -1)/9)*((10^n -1)/9 +1)/2 (n-th term is the middle 2(n-1) digits of the (n+9)-th term for n > 1).
Terms
- a(0) =1a(1) =66a(2) =6216a(3) =617716a(4) =61732716a(5) =6172882716a(6) =617284382716
External references
- oeis: A003555