Nonprime numbers whose sum of proper divisors is a power of 4.

Terms

a(0) =9a(1) =12a(2) =26a(3) =56a(4) =76a(5) =122a(6) =332a(7) =992a(8) =2042a(9) =3344a(10) =4336a(11) =8186a(12) =16256a(13) =32762a(14) =227744a(15) =266176a(16) =269072a(17) =299576a(18) =856544a(19) =2097146a(20) =5385812a(21) =8388602a(22) =16580864a(23) =17895664a(24) =19173944a(25) =33554426a(26) =61008020a(27) =67100672a(28) =201931760a(29) =1074789376