Product of primes appearing in the factorization of n! with even exponents.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =6a(7) =6a(8) =3a(9) =3a(10) =30a(11) =30a(12) =10a(13) =10a(14) =35a(15) =21a(16) =21a(17) =21a(18) =42a(19) =42a(20) =210a(21) =10a(22) =55a(23) =55a(24) =330a(25) =330a(26) =2145a(27) =715a(28) =5005a(29) =5005