25769869312domain: NAppears in sequencesa(n) is the sum of all integers from 2^(n-2)+1 to 2^(n-1).at n=17A049775Expansion of x*(1+5*x)/((1+2*x+1)*(1-4*x)).at n=18A117110a(n) = ((2^n)*((2^n)+1) - (2^(n-1))*((2^(n-1))+1))/2, a(1)=3.at n=17A158561