Сompute a trio of three binomial sums containing floor functions: sum_(k=0)^(lfloorn/3rfloor)((n),(3k)); sum_(k=0)^(lfloorn/3rfloor)((n),(3k+1)); sum_(k=0)^(lfloorn/3rfloor)((n),(3k+2))

Beckett Henry

Beckett Henry

Answered question

2022-09-04

Сompute a trio of three binomial sums containing floor functions:
k = 0 n 3 ( n 3 k )
k = 0 n 3 ( n 3 k + 1 )
k = 0 n 3 ( n 3 k + 2 )

Answer & Explanation

Anabelle Guzman

Anabelle Guzman

Beginner2022-09-05Added 14 answers

Step 1
Let a n be your first summation, and bn,cn be the second and third. Start by computing these exactly for small values of n. You should start to notice a general pattern emerging. Describe the pattern exactly, then prove that it holds in general using induction on n. Use the base cases
a 0 = 1 , b 0 = 0 , c 0 = 0
and the rules
a n + 1 = a n + c n , b n + 1 = b n + a n , c n + 1 = c n + b n
The rule a n + 1 = a n + c n can be proven by applying Pascal's identity to each summand in a n + 1 , and then splitting into two summations, which will be exactly a n and c n .

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