a(n) = c([ n/2 ]) + c([ n/3 ]) + ... + c([ n/n ]) for n >=3, where a(1) = 1, a(2) = 3 and c(n) = n-th number not in sequence a( ).

A023420

a(n) = c([ n/2 ]) + c([ n/3 ]) + ... + c([ n/n ]) for n >=3, where a(1) = 1, a(2) = 3 and c(n) = n-th number not in sequence a( ).