Alternating sum of heptagonal pyramidal numbers.

Terms

a(0) =0a(1) =-1a(2) =7a(3) =-19a(4) =41a(5) =-74a(6) =122a(7) =-186a(8) =270a(9) =-375a(10) =505a(11) =-661a(12) =847a(13) =-1064a(14) =1316a(15) =-1604a(16) =1932a(17) =-2301a(18) =2715a(19) =-3175a(20) =3685a(21) =-4246a(22) =4862a(23) =-5534a(24) =6266a(25) =-7059a(26) =7917a(27) =-8841a(28) =9835a(29) =-10900