a(n) = 3*2^n*(2^n-1) + 1.

Terms

a(0) =1a(1) =7a(2) =37a(3) =169a(4) =721a(5) =2977a(6) =12097a(7) =48769a(8) =195841a(9) =784897a(10) =3142657a(11) =12576769a(12) =50319361a(13) =201302017a(14) =805257217a(15) =3221127169a(16) =12884705281a(17) =51539214337a(18) =206157643777a(19) =824632147969