phi(p-1), as p runs through the primes.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =4a(5) =4a(6) =8a(7) =6a(8) =10a(9) =12a(10) =8a(11) =12a(12) =16a(13) =12a(14) =22a(15) =24a(16) =28a(17) =16a(18) =20a(19) =24a(20) =24a(21) =24a(22) =40a(23) =40a(24) =32a(25) =40a(26) =32a(27) =52a(28) =36a(29) =48