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MISCELLANEOUS EXERCISE 4 (II) · Q113

Q.Prove the following by using method of induction: 152n−1+115^{2n-1}+1 is divisible by 1616, for all n∈Nn \in N.

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Let P(n):152n−1+1=16mP(n):15^{2n-1}+1=16m. Base: n=1n=1: 151+1=16=16(1)15^1+1=16=16(1); holds. Hypothesis: assume 152k−1+1=16m15^{2k-1}+1=16m, i.e. 152k−1=16m−115^{2k-1}=16m-1. Step: 152(k+1)−1+1=152k+1+1=152k−1⋅152+1=(16m−1)(225)+1=3600m−225+1=3600m−224=16(225m−14)15^{2(k+1)-1}+1=15^{2k+1}+1=15^{2k-1}\cdot15^2+1=(16m-1)(225)+1=3600m-225+1=3600m-224=16(225m-14), a multiple of 16 (using $3600=16\times225 …

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