Number of ways to write n as an ordered sum of 1s, 2s, 3s and 4s such that no 2 precedes any 1 and no 3 precedes any 1 or 2.
A123569
Number of ways to write n as an ordered sum of 1s, 2s, 3s and 4s such that no 2 precedes any 1 and no 3 precedes any 1 or 2.
Terms
- a(0) =1a(1) =2a(2) =3a(3) =5a(4) =7a(5) =12a(6) =17a(7) =26a(8) =37a(9) =57a(10) =80a(11) =119a(12) =168a(13) =247a(14) =346a(15) =503a(16) =705a(17) =1014a(18) =1417a(19) =2026a(20) =2827a(21) =4015a(22) =5595a(23) =7912a(24) =11009a(25) =15505a(26) =21554a(27) =30260a(28) =42020a(29) =58837
External references
- oeis: A123569