Sum of divisors of n, sigma(n) (A000203), is a power of number of divisors of n, d(n) (A000005).

Terms

a(0) =1a(1) =3a(2) =7a(3) =31a(4) =127a(5) =217a(6) =889a(7) =2667a(8) =3937a(9) =8191a(10) =27559a(11) =57337a(12) =131071a(13) =172011a(14) =253921a(15) =524287a(16) =917497a(17) =1040257a(18) =1777447a(19) =3670009a(20) =4063201a(21) =11010027a(22) =12189603a(23) =16252897a(24) =16646017a(25) =66584449a(26) =113770279a(27) =116522119a(28) =225735769a(29) =677207307