Primes not occurring as |differences| in Cald's sequence A006509.

Terms

a(0) =641a(1) =1213a(2) =2617a(3) =2957a(4) =3727a(5) =5443a(6) =9283a(7) =17359a(8) =33829a(9) =66173a(10) =131303a(11) =264763a(12) =494743a(13) =957547a(14) =1888157a(15) =3753647a(16) =7490797a(17) =14961157a(18) =29899357a(19) =59773871a(20) =119551489a(21) =239106347a(22) =478234723a(23) =956607929a(24) =1913366111a(25) =3826828409a(26) =7653840367a(27) =15308666783a(28) =30619196381a(29) =57415599151