Imaginary part of (1+2i)^n.

Terms

a(0) =0a(1) =2a(2) =4a(3) =-2a(4) =-24a(5) =-38a(6) =44a(7) =278a(8) =336a(9) =-718a(10) =-3116a(11) =-2642a(12) =10296a(13) =33802a(14) =16124a(15) =-136762a(16) =-354144a(17) =-24478a(18) =1721764a(19) =3565918a(20) =-1476984a(21) =-20783558a(22) =-34182196a(23) =35553398a(24) =242017776a(25) =306268562a(26) =-597551756a(27) =-2726446322a(28) =-2465133864a(29) =8701963882