Euler totient function of Cullen numbers (A002064), n*2^n +1.

Terms

a(0) =1a(1) =2a(2) =6a(3) =20a(4) =48a(5) =132a(6) =240a(7) =528a(8) =1364a(9) =4180a(10) =7560a(11) =20784a(12) =42768a(13) =70992a(14) =151632a(15) =446208a(16) =986880a(17) =1688400a(18) =4006800a(19) =6080256a(20) =13843440a(21) =42125380a(22) =79567488a(23) =152712000a(24) =292573440a(25) =526051328a(26) =797636448a(27) =2942476992a(28) =7257012896