Triangle of coefficients in expansion of (3+7x)^n.

Terms

a(0) =1a(1) =3a(2) =7a(3) =9a(4) =42a(5) =49a(6) =27a(7) =189a(8) =441a(9) =343a(10) =81a(11) =756a(12) =2646a(13) =4116a(14) =2401a(15) =243a(16) =2835a(17) =13230a(18) =30870a(19) =36015a(20) =16807a(21) =729a(22) =10206a(23) =59535a(24) =185220a(25) =324135a(26) =302526a(27) =117649a(28) =2187a(29) =35721