[ exp(3/7)*n! ].

Terms

a(0) =1a(1) =3a(2) =9a(3) =36a(4) =184a(5) =1105a(6) =7736a(7) =61893a(8) =557043a(9) =5570436a(10) =61274803a(11) =735297637a(12) =9558869287a(13) =133824170031