Nialpdromes: digits in base 4 are in nonincreasing order.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =4a(5) =5a(6) =8a(7) =9a(8) =10a(9) =12a(10) =13a(11) =14a(12) =15a(13) =16a(14) =20a(15) =21a(16) =32a(17) =36a(18) =37a(19) =40a(20) =41a(21) =42a(22) =48a(23) =52a(24) =53a(25) =56a(26) =57a(27) =58a(28) =60a(29) =61