olymmath

Putnam 1990 A1

  • Session A

Let T0=2,T1=3,T2=6,T_0 = 2, T_1 = 3, T_2 = 6, and for n≥3n \geq 3, Tn=(n+4)Tn−1−4nTn−2+(4n−8)Tn−3.T_n = (n+4)T_{n-1} - 4n T_{n-2} + (4n-8) T_{n-3}. The first few terms are 2,3,6,14,40,152,784,5168,40576.2, 3, 6, 14, 40, 152, 784, 5168, 40576. Find, with proof, a formula for TnT_n of the form Tn=An+BnT_n = A_n + B_n, where {An}\{A_n\} and {Bn}\{B_n\} are well-known sequences.

Curated text Kedlaya Putnam archive. Quoted with source.

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