a(n)=(5-(-1)^n-6*n)*2^(n-2).

Terms

a(0) =1a(1) =0a(2) =-8a(3) =-24a(4) =-80a(5) =-192a(6) =-512a(7) =-1152a(8) =-2816a(9) =-6144a(10) =-14336a(11) =-30720a(12) =-69632a(13) =-147456a(14) =-327680a(15) =-688128a(16) =-1507328a(17) =-3145728a(18) =-6815744a(19) =-14155776a(20) =-30408704a(21) =-62914560a(22) =-134217728a(23) =-276824064a(24) =-587202560a(25) =-1207959552a(26) =-2550136832