a(n) = a(n-1) + a(n - 1 minus the number of terms of a(k) == (mod 5) so far).

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =9a(6) =14a(7) =23a(8) =28a(9) =51a(10) =74a(11) =125a(12) =153a(13) =181a(14) =306a(15) =380a(16) =686a(17) =839a(18) =992a(19) =1372a(20) =1678a(21) =2517a(22) =3203a(23) =4042a(24) =5720a(25) =7092a(26) =8464a(27) =10142a(28) =12659a(29) =18379