(Odd primes - 1)/2.

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =6a(5) =8a(6) =9a(7) =11a(8) =14a(9) =15a(10) =18a(11) =20a(12) =21a(13) =23a(14) =26a(15) =29a(16) =30a(17) =33a(18) =35a(19) =36a(20) =39a(21) =41a(22) =44a(23) =48a(24) =50a(25) =51a(26) =53a(27) =54a(28) =56a(29) =63