Euler totient function (A000010) of 2^n - 1.

Terms

a(0) =1a(1) =2a(2) =6a(3) =8a(4) =30a(5) =36a(6) =126a(7) =128a(8) =432a(9) =600a(10) =1936a(11) =1728a(12) =8190a(13) =10584a(14) =27000a(15) =32768a(16) =131070a(17) =139968a(18) =524286a(19) =480000a(20) =1778112a(21) =2640704a(22) =8210080a(23) =6635520a(24) =32400000a(25) =44717400a(26) =113467392a(27) =132765696a(28) =533826432a(29) =534600000