Number of trees on n nodes with forbidden limbs.

Terms

a(0) =0a(1) =1a(2) =1a(3) =1a(4) =2a(5) =2a(6) =4a(7) =7a(8) =16a(9) =30a(10) =68a(11) =146a(12) =340a(13) =786a(14) =1878a(15) =4507a(16) =11045a(17) =27220a(18) =67956a(19) =170766a(20) =432818a(21) =1103539a(22) =2831814a(23) =7303966a(24) =18934866a(25) =49302321a(26) =128910528a(27) =338329555a(28) =891099316a(29) =2354613762