a(n) = 2^(n*(n-1)/2).A006125a(n) = 2^(n*(n-1)/2).Terms a(0) =1a(1) =1a(2) =2a(3) =8a(4) =64a(5) =1024a(6) =32768a(7) =2097152a(8) =268435456a(9) =68719476736External referencesoeis: A006125