a(n) = round(e^(Pi*sqrt(n))).

Terms

a(0) =1a(1) =23a(2) =85a(3) =231a(4) =535a(5) =1124a(6) =2198a(7) =4072a(8) =7228a(9) =12392a(10) =20632a(11) =33506a(12) =53252a(13) =83048a(14) =127359a(15) =192401a(16) =286751a(17) =422151a(18) =614552a(19) =885480a(20) =1263795a(21) =1787960a(22) =2508952a(23) =3493970a(24) =4831164a(25) =6635624a(26) =9056943a(27) =12288744a(28) =16580631a(29) =22253151