Sum of the divisors of 4^n-1.

Terms

a(0) =4a(1) =24a(2) =104a(3) =432a(4) =1536a(5) =8736a(6) =22528a(7) =111456a(8) =473600a(9) =1999872a(10) =5909760a(11) =38054016a(12) =89522176a(13) =462274560a(14) =2015330304a(15) =7304603328a(16) =22907191296a(17) =166290432000a(18) =366506672128