Difference between 4^n and the nearest triangular number.

Terms

a(0) =0a(1) =1a(2) =1a(3) =-2a(4) =3a(5) =-11a(6) =1a(7) =-87a(8) =-167a(9) =-306a(10) =-500a(11) =-552a(12) =688a(13) =-3041a(14) =-579a(15) =20854a(16) =37075a(17) =55618a(18) =37108a(19) =-222296a(20) =-147729a(21) =891994a(22) =602155a(23) =-3523022a(24) =-2228805a(25) =14811346a(26) =11792251a(27) =-47737262a(28) =-1136517a(29) =375078994