64963domain: NAppears in sequencesa(n) = Sum_{k=0..n-3} T(n,k) * T(n,k+3), with T given by A026769.at n=6A027242Form a triangle with the numbers [0..n] on the base, where each number is the sum of the two below; a(n) is the number of different possible values for the apex.at n=13A066411a(n) = prime(n) * prime(2*n-1).at n=38A219603