a(n) = 1*2*3 - 4*5*6 + 7*8*9 - 10*11*12 + 13*14*15 - ... + (up to n).

Terms

a(0) =1a(1) =2a(2) =6a(3) =2a(4) =-14a(5) =-114a(6) =-107a(7) =-58a(8) =390a(9) =380a(10) =280a(11) =-930a(12) =-917a(13) =-748a(14) =1800a(15) =1784a(16) =1528a(17) =-3096a(18) =-3077a(19) =-2716a(20) =4884a(21) =4862a(22) =4378a(23) =-7260a(24) =-7235a(25) =-6610a(26) =10290a(27) =10262a(28) =9478a(29) =-14070