Floor[ Sum_{1..n} 1/i ]^n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =16a(4) =32a(5) =64a(6) =128a(7) =256a(8) =512a(9) =1024a(10) =177147a(11) =531441a(12) =1594323a(13) =4782969a(14) =14348907a(15) =43046721a(16) =129140163a(17) =387420489a(18) =1162261467a(19) =3486784401a(20) =10460353203a(21) =31381059609a(22) =94143178827a(23) =282429536481a(24) =847288609443