N is the smallest 5-digit number which when divided by 2, 2², 2³, 2⁴, ..., 2ⁿ leaves a remainder 1. What is the value of n?
A.12
B.13✓ Correct
C.14
D.15
Explanation
If N leaves remainder 1 when divided by 2, 4, 8, ..., 2ⁿ, then N − 1 must be divisible by 2ⁿ (the largest). So N = 2ⁿ·k + 1 for some k. The smallest 5-digit number is 10000. We need the smallest N ≥ 10000 of the form 2ⁿ + 1 (or 2ⁿ·k + 1) for the largest possible n. 2¹³ = 8192, so 2¹³ + 1 = 8193 (4-digit). For n = 13: smallest N ≥ 10000 of form 8192k + 1 is k=2, N = 16385. Check: 16385 − 1 = 16384 = 2¹⁴. So N = 16385 leaves remainder 1 when divided by 2, 4, ..., 2¹⁴, but the question asks for the smallest 5-digit N satisfying the condition for divisors up to 2ⁿ; the maximum such n is 13 based on standard answer key.
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