Number of (w,x,y,z) with all terms in {1,...,n} and w > x < y >= z.

Terms

a(0) =0a(1) =0a(2) =2a(3) =13a(4) =45a(5) =115a(6) =245a(7) =462a(8) =798a(9) =1290a(10) =1980a(11) =2915a(12) =4147a(13) =5733a(14) =7735a(15) =10220a(16) =13260a(17) =16932a(18) =21318a(19) =26505a(20) =32585a(21) =39655a(22) =47817a(23) =57178a(24) =67850a(25) =79950a(26) =93600a(27) =108927a(28) =126063a(29) =145145