Number of trees on n nodes with forbidden limbs.

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =19a(5) =73a(6) =297a(7) =1256a(8) =5467a(9) =24368a(10) =110610a(11) =509715a(12) =2377978a(13) =11210451a(14) =53318599a(15) =255537199a(16) =1232866889a(17) =5982965779a(18) =29185293329a(19) =143026402189a(20) =703829126231