Quadrinomial coefficients.

Terms

a(0) =2a(1) =12a(2) =40a(3) =101a(4) =216a(5) =413a(6) =728a(7) =1206a(8) =1902a(9) =2882a(10) =4224a(11) =6019a(12) =8372a(13) =11403a(14) =15248a(15) =20060a(16) =26010a(17) =33288a(18) =42104a(19) =52689a(20) =65296a(21) =80201a(22) =97704a(23) =118130a(24) =141830a(25) =169182a(26) =200592a(27) =236495a(28) =277356a(29) =323671