Version 1 of the "previous prime" function: largest prime <= n.

Terms

a(0) =2a(1) =3a(2) =3a(3) =5a(4) =5a(5) =7a(6) =7a(7) =7a(8) =7a(9) =11a(10) =11a(11) =13a(12) =13a(13) =13a(14) =13a(15) =17a(16) =17a(17) =19a(18) =19a(19) =19a(20) =19a(21) =23a(22) =23a(23) =23a(24) =23a(25) =23a(26) =23a(27) =29a(28) =29a(29) =31