Brilli the ant has thought up a diabolical sequence of integers an. It has initial values a1=1 and a2=3. Subsequent terms are given by
an=(n+1)an−1−nan−2 for n≥3.
Brilli the ant wants to know, how many integer values of n from 1 to 1000 (inclusive) are there such that an is a multiple of 11?
Your answer seems reasonable.
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