Numerator of 1 - (3/4)^n - frac((3/2)^n), where frac(x) = x - floor(x).

Terms

a(0) =0a(1) =-1a(2) =3a(3) =13a(4) =159a(5) =173a(6) =1767a(7) =12789a(8) =17759a(9) =126237a(10) =292183a(11) =1930245a(12) =3724303a(13) =23940141a(14) =14206087a(15) =99585429a(16) =640559295a(17) =12562430525a(18) =7042526903a(19) =43417422885a(20) =813747135599a(21) =494896655693