Sum of divisors of Woodall (or Riesel) numbers; sigma(A003261(n)); sigma(n*2^n - 1).

Terms

a(0) =1a(1) =8a(2) =24a(3) =104a(4) =216a(5) =384a(6) =1080a(7) =2160a(8) =4896a(9) =13656a(10) =32552a(11) =51312a(12) =137160a(13) =287408a(14) =573600a(15) =1999872a(16) =3034368a(17) =4778400a(18) =11098080a(19) =20984560a(20) =49533120a(21) =137218560a(22) =294000768a(23) =417361152a(24) =958698064a(25) =1755253280a(26) =4362821232a(27) =10552800000