21298376domain: NAppears in sequencesa(n) = a(1) + a(2) + ... + a(n-1) - a(m) for n >= 3, where m = 2*n - 3 - 2^(p+1) and p is the unique integer such that 2^p < n-1 <= 2^(p+1), with a(1) = a(2) = 1.at n=27A049884