Second differences of A130624.

Terms

a(0) =3a(1) =3a(2) =4a(3) =9a(4) =21a(5) =44a(6) =87a(7) =171a(8) =340a(9) =681a(10) =1365a(11) =2732a(12) =5463a(13) =10923a(14) =21844a(15) =43689a(16) =87381a(17) =174764a(18) =349527a(19) =699051a(20) =1398100a(21) =2796201a(22) =5592405a(23) =11184812a(24) =22369623a(25) =44739243a(26) =89478484a(27) =178956969a(28) =357913941a(29) =715827884