a(n) = n*x^n + (n-1)*x^(n-1) + . . . + x + 1 for x=2.

Terms

a(0) =1a(1) =3a(2) =11a(3) =35a(4) =99a(5) =259a(6) =643a(7) =1539a(8) =3587a(9) =8195a(10) =18435a(11) =40963a(12) =90115a(13) =196611a(14) =425987a(15) =917507a(16) =1966083a(17) =4194307a(18) =8912899a(19) =18874371a(20) =39845891a(21) =83886083a(22) =176160771a(23) =369098755a(24) =771751939a(25) =1610612739a(26) =3355443203a(27) =6979321859a(28) =14495514627a(29) =30064771075