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

Terms

a(0) =4a(1) =12a(2) =36a(3) =180a(4) =1260a(5) =252a(6) =252a(7) =2772a(8) =69300a(9) =900900a(10) =900900a(11) =15315300a(12) =15315300a(13) =290990700a(14) =290990700a(15) =6692786100a(16) =46849502700a(17) =46849502700a(18) =46849502700a(19) =46849502700