a(n) = 4*a(n-1) - n - 1, for n > 0, a(0) = 1.

Terms

a(0) =1a(1) =2a(2) =5a(3) =16a(4) =59a(5) =230a(6) =913a(7) =3644a(8) =14567a(9) =58258a(10) =233021a(11) =932072a(12) =3728275a(13) =14913086a(14) =59652329a(15) =238609300a(16) =954437183a(17) =3817748714a(18) =15270994837a(19) =61083979328a(20) =244335917291a(21) =977343669142