Fibonacci-type Custom Difference Sequence
GMAT glossary · Playbook
Definition
Generate or anchor a recurrence a_n = p a_n-1 + q a_n-2 until the asked term or cycle appears.
Fibonacci-type Custom Difference Sequence in plain English
Pull Fibonacci-type Custom Difference Sequence when each term is a fixed linear mix of the previous two (Fibonacci-like). Clues include Each term is the sum of the previous two, custom recurrence. Blueprint: Write a_n=pa_n-1+qa_n-2. Generate until a cycle appears, or use the Variable Anchor if a middle term is known. Why it beats the long way: Treating it as a plain arithmetic sequence ignores the two-term memory. Micro-example: Rule a_n = a_n-1 + 2a_n-2 with a_1=1, a_2=1: a_3=1+2· 1=3, a_4=3+2· 1=5, a_5=5+2· 3=11. Generate until a cycle appears, or anchor a known middle term and solve.
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