Negative of numerator of Sum_{k=1..n} (-1)^k / semiprime(k).

Terms

a(0) =1a(1) =1a(2) =7a(3) =17a(4) =209a(5) =25a(6) =37a(7) =281a(8) =9797a(9) =92711a(10) =120011a(11) =1589737a(12) =2027317a(13) =30861373a(14) =38322673a(15) =735926129a(16) =6107595203a(17) =5188977503a(18) =6040786643a(19) =5218865543a(20) =174771852097